US3801228A

US3801228A - Fuel pump control system and method

Info

Publication number: US3801228A
Authority: US
Inventors: M Mueller
Original assignee: TRW Inc
Current assignee: Nippon Paint Co Ltd; Northrop Grumman Space and Mission Systems Corp
Priority date: 1972-01-26
Filing date: 1972-01-26
Publication date: 1974-04-02
Anticipated expiration: 1991-04-02
Also published as: DE2300194A1; DE2300194C3; FR2169244B1; DE2300194B2; GB1400807A; JPS4884301A; FR2169244A1; SE380070B

Abstract

An internal control system for parallel pump fluid pumping systems. The control system acts to open a low-pressure pathway receiving the discharge from at least one of the pumps in response to internally sensed outlet requirements. The open pathway results in recirculation of low-pressure pumped fluid through a portion of the system while the outlet is supplied from another of the parallel pumps. The control system operates by sensing pressure from various points within the fluid system.

Description

United States Patent 1 Mueller FUEL PUMP CONTROL SYSTEM AND METHOD [75] Inventor: Milton W. Mueller, Cleveland, Ohio [73] Assignee: TRW Inc., Cleveland, Ohio [22] Filed: Jan. 26, 1972 21 Appl. No.: 220,782

[52] U.S. Cl. 417/282, 60/3928 R, 137/115, 417/286 [51] Int. Cl F04b 49/00 [58] Field of Search 417/282, 286, 288; 137/115; 60/3928 R [56] References Cited UNITED STATES PATENTS 2,780,172 2/1957 Coar 417/286 X 2,989,066 6/1961 Norlin 137/115 2,740,469 4/1956 Colestock 417/286 X Apr. 2, 1974 2,865,166 12/1958 Holbrook ..l37/115X Primary Examiner--Carlton R. Croyle Assistant Examiner-Richard J. Sher Attorney, Agent, or FirmHill, Gross, Simpson, Van

Santen, Steadman, Chiara & Simpson [57] ABSTRACT An internal control system for parallel pump fluid pumping systems. The control system acts to open a low-pressure pathway receiving the discharge from at least one of the pumps in response to internally sensed outlet requirements. The open pathway results in recirculation of low-pressure pumped fluid through a portion of the system while the outlet is supplied from another of the parallel pumps. The control system operates by sensing pressure from various points within the fluid system.

15 Claims, 3 Drawing Figures PATENIEDAPR 21974 SHEET 1 0F 2 I I I I I -za5l J FUEL PUMP CONTROL SYSTEM AND METHOD BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to fluid control systems and more particularly to a control system for a multi-pump fluid flow system.

2. Prior Art Fluid pumping systems, and particularly those systems used to pump fuel in modern aircraft, often require a pumping system capable of delivering the pumped fluid over a wide range of flows and operating pressures. In order to accommodate this, particularly in aircraft systems, the pumping systems normally comprise two or more pumps arranged in parallel, which function together-as a main pumping system. The systems generally also include a booster pump located at or near the fuel tank to provide a pressured flow of fuel to an interstage which feeds to the parallel ranked pumps.

Because ofthe necessity of delivering the output from the main pumping system at a wide range of flows, the system at times will be required to operate near maximum capacity, while at other times, such as when engine demand reduces the need for large quantities of fuel, the pumping system will have considerable overcapacity.

In standard systems, the booster pump is engine driven, and is normally a centrifugal pump whose rotational speed is directly proportional to the speed of the engine. However, the main pumping system pumps are normally positive displacement gear or vane pumps which operate at a constant speed. Because of this, the

displacement available in the main pumping system is generally constant. Thus, when engine demand for fuel slackens, the system is doing unnecessary work. This work is a function, not only of the displacement of the pumps, but also of the pressure at which the pump outlet delivers the pumped fluid.

It has, heretofore, been suggested to accommodate the differing flow demands by providing high pressure relief valves downstream of the ranked pumps, which relief valves recognize the existence of abnormal high pressures downstream of the pumps when engine demand for fuel is. lessened, and open a bypass shunting a portion of the pumped fuel to an area upstream of the pumps. While such systems accommodate, to a limited extent, the necessary fuel flow variations within the system, they do'so at the expense of adding excess work in that the outlet from the main pumping system must, of necessity, still be at high pressure.

The extra work performed on the fluid being pumped has the disadvantage of raising the temperature of the pumped fluid. Since it is common to use the pumped fluid or fuel as a coolant for the engine oil, by shunting it through engine oil coolers, any unnecessary rise in the temperature of the fuel reduces the effectiveness of the system.

Other attempted solutions have relied upon external controls to shut down one or more of the main stage pumps. Such systems are undesirable, first, because they require external controls to the pumping system, which controls normally require electric source connections in the highly dangerous fuel handling system; secondly, because the use of systems capable of shut- .ting down one or more of the pumps allows failure of the output from one or more of the pumps to an area upstream of the pumps, has required external controlling to open a valve. Such external controlling is undesirable and, further,-generally requires the use of hazardous electrical connections and sensing equipment.

SUMMARY My invention overcomes the disadvantages of the prior art and provides a low-pressure escape path for fluid pumped by one or more of a ranked system of parallel pumps. The low pressure escape path is controlled by a valve which in turn is controlled by a sensing system operating entirely interior of the pumping system.

The sensing system of my invention does not require any electrical connections or' external input.

For descriptive purposes, the system will be described in connection with a two-pump main stage system, however, the control system is adaptable for use in any multi-parallel pump system. The main pumps are fed from a common interstage and discharge into conduits to a common output line. The conduit from one of the pumps is connected with a bypass conduit for receiving the output from the one pump and channeling it back to the interstage. A pressure balanced valve is interposed in the bypass conduit controlling flow therethrough. The pressure balanced valve is cyclable to an open position by means of a controlled discharge from one section of the pressure balanced valve. The discharge path is open or closed in response to a number of sensing valves positioned in series in the discharge line. The valves sense pressures internally within the fluid flow system and are open or closed in relation to those pressures.

Thus, when conditions within the system are right, that is when engine demand for fuel is lessened to a point when the non-bypassedor noncontrolled pump alone can supply sufficient fuel, the sensing valves will open, allowing the bypass conduit valve to become un balanced, thereby opening the bypass. Because the bypass valve opens fully, and maintains its open state against a low pressure, the bypass is a low-pressure bypass, thereby reducing the amount of work performed by the one pump.

In the embodiments illustrated, the conditions sensed by the sensing valves include engine speed as a function of booster pump input-output, pressure differential, internal fluid flow to the main stage pumps, and output from the non-bypassed pump.

In a preferred embodiment, axially moving spool pilot valves are used for some of the sensing valves while an axially moving sleeve valve is mechanically coupled with a check valve for another of the sensing valves. In another preferred embodiment, diaphragms attached to a valve closure member are used, the diaphragms sensing the pressure changes and moving the valve closure member in relation thereto.

- It is therefore an object of this invention to provide a pumped fluid control system. i

It is a further object of this invention to provide a pumped fluid control system for parallel fuel pumping systems. I

It is another object of this invention to provide a pumped fluid control system for parallel pump fuel systems wherein the output from one or more of the parallel pumps is bypassed at low pressure to an interstage feeding the pumps.

It is another object of this invention to provide a control system for a pumped fluid system allowing a lowpressure bypass to open downstream of a pump in response to a sensing of internal conditions.

It is yet another object of this invention to provide a control system for pumped fluid, the control system being independent of any external stimuli and responsive to internal conditions sensed within the pumping system. i

It is another object of this invention to provide a pumped fluid control system for parallel pump pumping systems, the control system opening a bypass downstream of one or more pumps, the control system actuated by sensing internal conditions within the fluid flow system.

' It is a more specific object of this invention to provide a control system for an aircraft fuel pumping system, the pumping system including two or more parallelmain pumps, the control system opening a bypass from at least one of the pumps, the bypass being controlled by a valve which in turn is actuated by a series of sensingdevices, the sensing devices responsive only to internal conditions within the pumping system.

It is'a specific object of this invention to provide a control system for aircraft fuel pumping systems which opens a bypass in response to conditions sensed within the fuel flow system, the control system sensing internal pressures from at least three different portions of the fuel flow system.

It is a general object of this invention to provide a method of bypassing the output of one or more pumps in an aircraft fuel supply system at low pressure in response to lessened engine demand.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects, features and advantages of the invention will be readily apparent from the following description of certain preferred embodiments thereof,

takenin conjunction with the accompanying drawings,

although variations and'modifications may be effected DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 schematically illustrates a system flow diagram for a two-pump main pumping system aircraft fuel supply system. The diagram illustrates the bypass and control system of this invention. Although only two main pumps are illustrated in parallel, it is to be understood that this system can be used with a multi-pump ranked parallel pumping system.

In the diagram illustrated in FIG. 1, the pumping sys- 5 tom includes an inlet 11 such as may connect with a fuel storage tank and an outlet 12 such as may discharge to an aircraft engine or the like, and/or to hydraulic actuators, oil coolers, and other utilizers of pressurized fuel. A secondary inlet 13 may return fuel from these sources. Numerous pressure and temperature taps, ports and valves 14 are also illustrated in the system.

The pumping system includes a main pumping stage 15 comprising parallel pumps 16 and I7, and a preliminary or boost pump stage 18 including a booster pump 19. The booster pump 19 is in communication with the inlet 11 through a conduit opening'20. The booster pump discharges to a conduit 21 which is communicated through a sleeve orifice valve'22 to a conduit 23 which discharges in turn to a conduit 24 communicating with an external device 25, such as a heater orthe like. The heater 25 is illustrated as communicating with aconduit-26 which in turn communicates with a prefilter conduit 27. A bypass 28 controlled by a pressure check valve 29 communicates the conduit 23 with the conduit 27, bypassing the external device 25, should that device become clogged or closed off. A filter unit 30 is positioned between the conduit 27 and a conduit 31 which in turn communicates to the interstage 32. A bypass conduit 33 communicates the conduit 27 to the interstage 32 and is controlled by, a pressure check valve 34 to bypass the filter 30 in case the filter 30 be-' comes clogged.

In case the boost pump 19 is inoperative or any of the conduits 21 through 31 becomes clogged, a bypass 34a communicates the inlet 11 through a' pressure check valve 35 to the interstage 32. A conduit 38 may also communicate the interstage 32 to the auxiliary inlet 13 through a pressure check valve 39'. The

valves

29, 34, 35 and 39 are all normally one-way valves and are common to prior art duel stage pump flow systems.

It can be seenfrom the above that in the normal course, all of the fluid supplied to the system through thence tothe interstage 3 2. The interstage 32 is in common communication 'with conduits 41 and 42 which in turn communicate with the intakes of pumps 16 and y 17.

Pumps

16 and 17, in aircraft'embodiments, are normally positive displacement gear or vane pumps which operate at constant speed. The booster pump 19 in the boost stage 18 is normally an engine-driven centrifugal pump. Therefore, the output from the boost stage is a function of engine speed. While the two main stage pumps 16 and 17 are illustrated as being substantially equal in size, it is to be understood that one of them, for example, 16, could be a larger pump in which case it would normally be considered the main pump while the other and smaller pump such as pump 17 would be an auxiliary pump. The main pumping stage 15 is sized to provide sufficient flow for maximum demands. Thus, when the engine is throttled down, the pumping stage will supply to conduit 50, which is in communication with the outlet 12, a greatenthan-necessary flow of the inlet is normally fed to the boostpump 19 and are normally spring-biased and require a positive pressure to open to communicate the

conduits

51 and 52 with the conduits 50. At the same time, they serve to prevent backflow in those situations where the pressure in the conduit 50 is greater than in either of the

conduits

51 and 52.

In order to provide relief within the conduit 50, when engine demand is slackened, a high-pressure relief valve 55 is provided communicating the conduit 50 with a pre-pump conduit such as the conduit 38 leading to the interstage 32. This communication is illustrated as being by means of conduit 56. The high-pressure relief valve 55 is also a one-way valve providing flow only from the conduit 50 to the conduit 38.

It will be appreciated that what has been described prior to this is a normal fuel flow diagram, with the exception of valve 22, commonly found in aircraft fuel supply systems. My invention, hereinafter described, is illustrated as being used with this diagram; however, it is adaptable for use with most multi-pump, parallel ranked pumping systems.

In the system above described, when engine demand slacks, excess pumping capacity in the main pumping stage results either in a greater flow through the system and return via the auxiliary inlet 13 or, in most cases, in a greater pressure in the outlet conduit 50. The greater pressure in the conduit 50 opens the valve 55, providing a return flow at high pressure. Thus, the pressure in the conduit 50 is maintained relatively high in order to maintain the valve 55 open. In such circumstances, the

parallel pumps

16 and 17 are doing considerable excess work. This will elevate the temperature of the fuel beyond the desired point.

In order to eliminate this problem, I have provided a bypass consisting of

conduits

60 and 61 which bypass the output from the pump 16 backto the interstage 32. Conduit 60 is in communication with conduit 51 at the outlet end of pump 16 and with conduit 61 which in turn communicates to interstage conduit 32. Interposed between

conduits

60 and 61 is valve 63 which controls the bypass. The valve 63 normally closes the connection between the

conduits

60 and 61, so that the output from the pump 16 passes through the valve 53 to the conduit 50, and thence through the outlet 12.

The valve 63 of this invention is a pressure-balanced valve which is'capable of remaining closed against high pressure, while at the same time capable of remaining open against a low pressure. Because the valve stays open when faced with a low pressure, the

bypass conduits

60, 61 will have a pressure approximating that of the interstage 32. Thus, the bypass of the output from the pump 16 will be at a low pressure, causing the valve 53 to close, assuring that the entirety of the output from the pump 16 is bypassed. In this way, the amount of useless work done by the pump 16 is minimized and the temperature rise of the fuel is kept minimal.

The valve 63 is controlled by sensing

devices

70, 71 and 72 which function together to open a drain conduit 74 communicating with one side 75 of the pressurebalanced valve 63. When the drainage conduit 74 is communicated with the side 75 of the valve enclosure, the pressure balance of the valve 63 will be eliminated and the valve will open. When the

sensing devices

70, 71, 72 are closed, the portion 75 of the valve enclosure for the valve 63 will be closed, and the valve 63 will close.

The

sensing devices

70, 71 and 72 sense only conditions within the pumping system itself intermediate the inlet 11 and the outlet 12. No external stimuli act upon the sensing devices.

In a preferred embodiment, each of the sensing devices is a pressure controlled valve having a portion interposed between the portion 75 of the valve enclosure and the drainage conduit 74. The pressures acting on the valve portion cause a passageway to open through each of the sensing devices. When all three sensing devices are open, the portion 75 of the valve enclosure will be in communication with the drainage conduit 74.

As illustrated in FIG. 1, the sensing devices may sense engine speed, pumping system internal fluid flow and auxiliary pump discharge pressure.

For example, the sensing device senses the auxiliary pump 17 discharge pressure via a pressure sensing passage a extending from the conduit 52 downstream of the pump 17 to the sensing device 70. This pressure is compared with the pressure in the conduit 61 via a pressure sensing conduit 76. With the valve 63 closed, the pressure in the conduit 61 will be the same as in the interstage 32. As long as the discharge pressure from the auxiliary stage pump 17 is maintained sufficiently high above the interstage pressure, typically 300 or 400 psi, the sensing device 70 will remain open to allow communication between the portion 75 of the valve enclosure and the nextsensing device 71.

The sensing device 71 senses engine speed by comparing the pressures between the inlet 11 via the pressure sensing passage 78 and the outlet or discharge from the boost pump as by the pressure sensing passage 79. The sensing passage 78 senses the pressure from adjacent the inlet upstream of the booster pump 19. The passage 79 senses the pressure at a point downstream of the booster pump but upstream of the main pumping stage. This is indicated in FIG. 1 as being a sensing passage between the sensing device 71 and the conduit 61, which is normally at a pressure equivalent to the interstage 32. Because the boost pump 19 is an enginedriven pump, the pressure output therefrom is proportional to the engine speed and a comparison of the pressure between the inlet to the pump and the outlet therefrom indicates the engine speed. When the engine speed is in the correct range, the sensing device 71 will open to provide a passageway from the sensing device 70 to the sensing device 72.

The sensing device 72, illustrated in FIG. 1, comprises a drainage path portion 72a and the sleeve orifice valve 22, with a mechanical connection indicated by the broken line 80 therebetween. The sleeve orifice valve 22 senses internal flow between the boost pump stage and the main pump stage. When the flow rate is low enough to indicate a lessened demand, the sensing device 72 will open a passage between the sensing device 71 and the drainage conduit 74. Thus, when all three sensing devices are open, the pressure balanced I valve 63 will be unbalanced and open to communicate the conduit 60 to the conduit 61, resulting in a bypass of the output from the pump 16 at low pressure.

FIGS. 2 and 3 illustrate two embodiments of the valve 63 and sensing controls 70, 71 and 72. In the first embodiment, illustrated in FIG. 2, the

sensing devices

70 and 71 comprise spool valves or pilot valves and the sensing device 72 comprises a ball check valve opened by the mechanical connection with the sleeve orifice valve 22.

in the embodiment illustrated in FIG. 3, the

sensing devices

70, 71 and 72 comprise movable diaphragms operating a needle stopper which in turn opens and closes a drainage path for the pressure-balanced valve 63. it is to be understood that these embodiments are only illustrative of an internal bypass control and that a greater or lesser number of sensing devices could be used which can sense other desired parameters.

Considering first the embodiment illustrated in FIG. 2, the figure illustrates a cross-sectional view of a portion of the pump housing which includes the bypass valve and sensing controls therefor.

The pump housing 90 includes portions of the conduit 21 from the boost pump outlet and the conduit 23 with the sleeve orifice valve 22 interposed therebetween. 1

The housing 90 also includes a portion of the conduit 60 in communication with the bypassed or controlled 'pump dischargeand the bypass conduit 61, with the pressure-balanced valve 63 controlling communication between the

conduits

60 and 61. The sensing controls 70 and 71 are illustrated as being axially movable spool valves while the control unit 72 consists of the sleeve orifice valve 22 and a ball check valve 193 positioned to be acted upon by the sleeve orifice valve 22.

As illustrated, the valve 63 has a cup-shaped valve body member 93 received in a tubular housing member 94, which has a passageway 95 at one end which passageway communicates with a drainage passage 96. The cup-shaped body member 93 is positioned interiorly of the tube-shaped member 94 and is biased by a spring 97 against a valve seat 98 formed on the inner diameter of the tubular member 94. The bottom wall 99 of the cup-shaped member 93 closes against the valve seat 98 at the juncture with the conduit 60 to block the conduit 60. Passageways 100 in'the tubular body portion 94 open to a conduit 101 in communication with the bypass conduit 61, downstream of the valve seat 98. Therefore, in order for the conduit 60 to communicate to the bypass conduit 61, the valve body 93 mustbe moved away from the valve seat 98 against the pressureof the spring 97. p

The end wall 99 of the cup-shaped body member 93 has an orifice or passageway 102 communicating with passageways 103 which open to the conduit 60 through a filter 104 which prevents clogging of the narrow passageways 103- and orifice 102. Because the orifice opens to the conduit, the interior 105 of the tubular body member 94 which is closed at itsouter end by a closure plate 106 against which the spring 97 backs and at its other end by the end wall 99 of the valve body 93, will have an interior pressure substantially equal to the pressure in the conduit 60 due to the bleed-through from the orifice 102. So long as the drainage opening 96 is blocked by the sensing controls 70, 71 and 72, the pressure in the area 105 will be equal to the pressure in the conduit 60. Therefore, the spring 97 will maintain the valve body 93 against the valve seat 98 to prevent communication between the conduit 60 and the bypass conduit 61. Communication between the area 105 and the bypass conduit 61 is prevented due to the sealing seat of the valve body 93 against the inner diameter of the tubular portion 94. However, whenever the age conduit 96 which communicates as at 74 to the conduit 23 downstream of the three

sensing devices

70, 71 and 72, the pressure within the area 105 will approximate' the pressure within the conduit 23 which is upstream of the pump 16. Therefore, the pressure in the conduit 60 will be sufficiently greater than the pressure in the area 105 to overcome the spring bias and open the valve 63, allowing communication between the conduit 60 and the bypass conduit 61. As long as the three sensing controls are open, this condition will continue inasmuch as the

drainage openings

95, 96 and 74 are of a greater size than the orifice 102.

As illustrated, the

sensing devices

70 and 71 are spool valves which are interposed in the drainage line 96. The valves each have a

cylindrical spool

109, 110 received within a tubular housing 111, 112, the tubular

housing having openings

113, 114 therethrough communicating the drainage passage 96 upstream of the

spool

109, 110 to the interior of the tube. The spool valves have circumferential grooves 116, 117 therein and the tubular housings have

inner diameter grooves

118, 119 communicating to discharge

openings

120, 122 downstream of the spool, the

discharge openings

120, 122 opening to the portion of the drainage conduit 96 downstream of the individual sensing control. When the

spool

109, 110 is moved axially so that the

inlet openings

113, 114 are communicated to the

grooves

118, 119 through the grooves 116, 117, the drainage conduit 96 vwill be open through the sensing controls. Both spool valves are moved by pressure acting against the axial ends of the spools 109, l 10, which pressure is offset by

springs

130, 131 acting against one of the drainage path 96 is open to a lower pressure area, in

this embodiment to the conduit 23 through the drainaxial ends of the spools. 1n the sensing control 71 which senses engine speed as a function of the difference between the boost pump intake pressure and outlet pressure, the axial ends of the tube 111 are communicated, at one end, with the conduit 79 which in turn is communicated with the conduit 21, thereby Sensing pressure downstream of the booster pump, the other end of the spool being communicated via conduit 78 with the inlet, thereby sensing inlet pressure. in this instance, the spring is interposed between a housing portion 134 and the axial end 135 of the spool open to the conduit 76. Therefore, the pressure downstream 'of the boost pump sensed by the conduit 79 must be sufficiently greater than the pressure prior to the boost pump sensed by the conduit 78 to overcome the bias of the spring 130 and move the spool axially to a point where the groove 116 communicates with both the sensing device inlet 113 and the sensing device outlet 118-120. The spool 109 is capable of moving within the tube 1.1 1 past that point to a point where the groove 116, while remaining in communication with the groove 118, is no longer in communication with the inlet 113. At this point, the conduit 96 will again be blocked by the sensing control 71. Thus, the sensing control 71 is open only for an intermediate stage of pressures. When the pressure of the boost pump discharge is low, indicating low engine speed, the spool valve 71 will be closed due to the action of the spring 130 and the inlet pressure 78 acting against the end 135 of the spool to push it to a point where the groove 116 is not in communication with the groove 118. As the boost pump pressure increases, the spring urging will be overcome and the groove 116 will enter into communication with the groove 118 while remaining in communication with the inlet opening 113. At this point, the discharge conduit 96 will be open through the control 71. As the engine speed continues to increase and the boost pump discharge pressure continues to increase, the spool 109 will be forced beyond the point of communication with the opening 113, thereby again closing the conduit 96 through the sensing control 71. By dimensioning of the grooves and spools and their spacing from one another, and by control of the tension of the spring, it is possible to set the control 71 to function only in a desired range of pressures, indicating a desired engine speed. For example, it is possible to set the spool valve so that it will remain closed at all speeds below 3,000 to 3,500 rpm. and at all speeds above 4,500 to 5,000 rpm. In this way, the control 71 will prevent bypass valve bleed flow except in engine speed ranges of approximately 3,500 to 4,500 r.p.m. Thus, only in those speed ranges can the bypass valve 63 open. Alternatively, of course, the valve can be designed so as to remain open below a given speed and to remain closed above that speed, as sensed as a function of boost pump discharge pressure.

The control 70 senses the output of the noncontrolled pump 17. In order to do this, one end of the spool 110 is open via conduit 76 to a prepumped passage such as the passage or conduit 21, thereby sensing pressure prior to the non-controlled pump 17 and control pump 16. The other end 140 of the spool 110 is open to conduit 75a which communicates with a post auxiliary pump conduit or non-controlled pump conduit such as the conduit 52 of FIG. 1. In this control, the spring 131 is interposed between the end 141 of the spool and the housing portion communicating to the conduit 76. Therefore, the pressure in the conduit 75a must be sufficiently greater than the pressure in the conduit 76 to overcome the bias of the spring 131 to move the spool to a point where the control inlet 114 is communicated with the control outlet 122 by an overlapping of the grooves 117, 119. The spool end 141 is dimensioned with respect to the housing end 143 adjacent the conduit opening 76, so that when the pressure in the conduit 75a is sufficiently great to overcome the spring 131 and pressure in the conduit 76, the valve will remain open by bottoming of the end 141 against the housing portion 143 to prevent further opening movement of the spool. Thus, the sensing control 70, unlike the illustrated sensing control 71, has only one open position and one closed position. The spool is prevented from moving axially a sufficient distance to close off communication between the inlet 114 and the groove 117. Thus, for all non-controlled pump discharges sufficiently large, the control 70 will be open. However, whenever the discharge pressures from the non-controlled pump falls below a given level of pressure rise over the pressure at the non-control pump inlet, the sensing'control 70 will close. This could occur due to failure of the non-control pump 17 or for other reasons such as greater engine usage of fuel creating a high flow, low-pressure discharge from the noncontrolled pump.

The sensing control 72 senses fuel flow within the system, in the illustrated embodiment prior to the main pumping section. The flow rate is sensed by a sleeve orifice valve 22. In the illustrated embodiment shown in FIG. 2, the flow through conduit 21 is in the direction of arrow 145 against the sleeve orifice valve 22. The sleeve orifice valve is a substantially I-I-shaped cross section valve body 146 having a cross member 147 blocking off the tubular interior 148 and preventing flow therethrough except through an orifice 149 in the cross member 147. Upstream of the cross member 147, radial openings 150 are provided and downstream of the cross member 147, radial openings 151 are provided. The outer surface of the valve body 146 is in sealing engagement with the wall 153 of the conduit in which it is received, except for a groove 154 in the surface of the conduit. The groove 154 is axially long enough to communicate the radial openings 150 to the radial openings 151 when the valve body is in a given position. The valve body 146 is axially movable in the conduit to close off communication with the groove 154 and the upstream openings 150. When this occurs, the only flow through the conduit 21-23 occurs through the orifice 149. A spring 156 acts against the valve to urge it in a direction to cut off communication between the openings 150 and the groove 154. The spring force is overcome by the pressure of the fluid in the conduit 21 acting against the cross member 147. Whenever the flow of fluid through the conduit 21 is sufficiently great, the valve 22 will remain open against the spring 156. As the flow of fluid decreases, the valve will close and all flow will. continue through the orifice 149. The spring 156 is sized to overcome the pressure drop caused by the cross member 147 and orifice 149 at low flow conditions to urge the valve body 22 against the seat 158, closing off communication between the openings 150 and the groove 154. As flow increases, the pressure drop across the cross member 147 through the orifice 149 will increase, and the spring pressure will be overcome, causing the valve 22 to open so that the openings 150 are in communication with the groove 154. By sizing the orifice 149 and the spring rate of the spring 156, the valve can be designed to remain closed at all flows below a given point, for example, 5 gallons per minute, and to remain open at all flows above that point. Preferably, the orifice 149 will be sized to accept all flows below that point with a very small pressure drop across the cross member 147. Thus, the spring 156 can have a low spring rate, requiring small pressures, for example on the order of 4 to 5 psi, to open. Thus, the valve does not preventfull flow conditions, and further, interferes very little with flow during low flow conditions.

The ball check valve 193 is positioned with respect to the valve 22 so that the lever arm 160 of the ball check is contacted by the valvebody 146 whenever the valve 22 is in a closed position. In such situations, the lever 160 will lift the ball 161 off of the valve seat 162 against the pressure in passage 96 and spring 194, thereby communicating the drainage passage 96 with the passage 74. When the valve 22 is in its full flow open position, the mechanical contact between the lever 160 and the valve body 146 cannot occur and the ball will remain seated against the valve closure seat 162, blocking off communication of the drainage passage 96. Thus, the sensing control 72, consisting of the sleeve orifice valve 22 and the ball check 93, which the passage 96 only during low flow conditions, such as would be encountered when the engine demand for fuel lessens.

As can be seen from the above description, in the embodiment illustrated in FIG. 2, the bypass control valve 63 can open only when the sensing control 70 senses that the engine speed is within a desired range; when the sensing control 71 senses that the auxiliary or noncontrolled pump discharge is sufficiently great to sup- FIG. 3 schematically illustrates another embodiment of this invention wherein the bypass valve 63 is controlled by a drainage conduit 74 blocked by a valve 200 against a valve seat 201. The valve 200 is controlled by three pressure-sensing diaphragms 70b, 71b and 72b. The diaphragms 71b and 72b are received in a housing chamber 204 and divide the chamber into three ar eas, an area 205 below the diaphragm 71b, an area 206' above the diaphragm 72b and an area 207 between the two-diaphragms. The area 205 below the diaphragm 71b is ported via a conduit 209 to the inlet 11 prior to the boost pump 19 so that the pressure in the area 205 is equal to the inlet pressure. The area 207 is ported via a conduit 210 to the conduit 21 downstream of the boost pump 19 so that the area 207 has a pressure equal to the pressure of the boost pump output. Therefore, the diaphragm 71b senses engine speed as a function of boost pump pressure rise. The spring 212 is disposed in the area 205 to ct on the diaphragm 71b which has an abutment nib 213, and urges the diaphragm 71b in an upward direction until the abutment nib 213 contacts theunderside of diaphragm 72b. When the pressure rise across the boost pump 19 is suff ciently great, the pressure in thearea 207 will be sufficiently larger than thepressure in the area 205 to counteract the force of the spring 212 and remove the influence of the abutment nib 213 from the diaphragm 72b by forcing the diaphragm 71b downwardly.

The diaphragm 72b has the valve 200 attached thereto for movement therewith so that as the diaphragm 72b moves upwardly and downwardly in the chamber 204, the diaphragm 72b moves the valve 200 between a seating and unseating relationship with the valve seat 201 to open and close the drain passage 74.

The diaphragm 72b is operatedas a function of engine fuel demand. Engine fuel demand is determined as a function of total new'fuel input to the pumping system by sensing the pressure drop across a restriction R1 in the conduit 23 downstream of the 'boost'pump and downstream of the connection between the conduits 21 and 210. The pressure downstream of the restriction R1 is ported via conduit line 216 to area 206. As engine fuel demands lessen, the pressure differential across the restriction R1 will change. As the pressure sensed by the line 216 increases, the resistance to downward movement of the valve 200 decreases.

Diaphragm 70b ,is received in housing chamber 218 and is attached to the valve 200, and movable therewith. The diaphragm 70b divides the chamber 218 into

areas

219 and 220. The area 220 senses pressure via a conduit 221 which is connected with conduit 42 downstream of a restriction R2. Conduit 42 is in turn connected to the intake to the non-controlled pump 17. Area 219 senses pressure in the interstage 32 via a conduit 225, which also forms part of the drain path 74 whenthe valve 200 is open. The diaphragm 70b then senses the flow generated by the positive displacement non-controlled pump 17, as a function of the pressure drop across the restriction R2 which pressure drop is thedifference between the pressure at the interstage 32 sensed by a conduit 225 and the inlet pressure to the pump 17 which pressure is sensed by the conduit 221.

A spring 230 acts against diaphragmb to force it and the valve 200 upwardly.

Therefore, it can be seenthat the seating of the valve 200 in the valve seat 201 is determined by the ratio of engine flow demand as measured by the differential pressure drop across the restriction R1, and noncontrolled pump output as measured by the difi'erential pressure drop across the restriction R2 acting on the diaphragms 72b and 70b respectively. In any case, where the pressure drop across R1 is larger than the pressure drop across R2, diaphragm 72b forces will overcome diaphragm 70b forces, and in conjunction with the spring 230, act to seat the valve 200 in the valve seat 201. This will always be the case when the engine fuel flow demand is sufficiently large relative to the auxiliary pump 17 flow capacity. However, when the engine flow demand drops and a portion of the discharge flow from both the

pumps

16 and 17 is bypassed through the relief valve 55 and the conduit 56 at high pressure back to the interstage 32, the pressures acting to retain the valve 200 seated against the valve seat 201 will lessen. As engine flow demand drops still further, the pressure drop ratio through R1, which measures total engine flow, or actual pump throughput, and R2, which measures the flow generated by the positive displacement auxiliary pump 17, will change until the pressure drop across R2 exceeds the drop across R1 by a predetermined amount. At this point, with a greater pressure in area 219 than in area 220 and with a small pressure differential between

areas

206 and 207, the pressure differential caused by the restriction R2 will act downwardly on the diaphragm 70b and will overcome the pressure differential across R1 acting upwardly on diaphragm 72b and the force of the spring 230 also acting upwardly and cause the valve 200 to lift off the seat 201. When this occurs, a drainage path is opened from the area 235 behind the end wall 236 of the bypass control valve 63. This area will then be allowed to drain through the drainage path 74 and the conduit 225. Therefore, the relatively large pressure in the conduit 60 will cause the valve 63 to open, communicating the conduit 60 to the bypass conduit 61. At this point, the pressure downstream of the check valve 53 will lessen to a point where the check valve 53 will close, thereby resulting in a recirculation of the output from the main pump 16 at a low pressure through the

bypass conduit

60, 61.

It can be seen from the above description that the embodiment illustrated in H0. 3 therefore senses engine speed as a function of the pressure differential between

areas

205 and 207, senses total fuel input as a function of the pressure differential between

areas

207, 206, and senses auxiliary or noncontrolled pump pressure as a function of the pressuredifference between

areas

219, 220. Thus, it is only when the pressures in the

areas

205, 206, 207, 219 and 220 are within preset ranges that the bypass valve can open.

It is to be appreciated that this system provides safety advantages, substantially the same as the safety advantages provided in the embodiment illustrated in FIG. 2. That is to say that if, for example, the boost pump 19 would fail, the control system would lose the pressure differential between the

areas

207 and 205 so that the spring 212 would maintain the valve 200 closed. Additionally, should the auxiliary or non-controlled pump 17 fail, the pressure drop across R2 would cease, and the spring 230 would maintain the valve closed. Additionally, other safety features are inherent in the designs illustrated.

It will be noted that in the embodiment illustrated in FIG. 3, the non-controlled pump discharge pressure is not sensed as in the system described in FIG. 2. This is because the direct sensing of the auxiliary or noncontrolled pump 17 flow generating capacity as a function of the pressure drop across R2 effectively senses the working of that pump.

It should be appreciated that although both of the preferred embodiments discussed herein sense three separate conditions, i.e., engine speed, non-controlled pump working, and engine fuel demand or flow rate, that if desired, a lesser number of functions can be sensed or, additional functions could be sensed, resulting in the addition of other valves or diaphragms controlling the bypass valve.

Although the teachings of my invention have herein been discussed with reference to specific theories and embodiments and although illustrative means for accomplishing explained results have been described, it is to be understood that these are by way of illustration only and that others may wish to utilize my invention in different designs or applications.

I claim as my invention:

l. A pump fluid control system comprising: a fluid pumping system including an inlet for receiving fluid, a booster pump in communication with said inlet and having an outlet in communication with an interstage, a main pump and at least one other pump connected in parallel between said interstage system, a control means for said pumping system for selectively diverting the main pump discharge to a bypass pathway and thereby remove the main pump discharge from the flow to the common outlet, said control means including a valve means for controlling flow inthe bypass pathway, said valve means including means for balancing the pressure acting on opposite side of a valve member thereof, said control means including means for sensing' only fluid pressure from at least three different areas of said pump system and means for unbalancing the pressure as one side of the valve member in response to the pressures sensed by said sensing means so that unbalancing the pressures as the valve member of the valve means causes the valve means to open and provide a low pressure bypass for the main pump.

2. A pump fluid control system according to claim 1, wherein said means for unbalancing including a drainage conduit ported to said one side of the valve member and second valve means for controlling flow in said conduit, said second valve means being actuated between a closed and open position by the application of pressure differentials from the pressures sensed by said sensing means.

3. A pump fluid control system according to claim 2, wherein said second valve means includes at least one spool valve which is axially shifted between an opened and closed position in response to pressure acting on an axial end thereof. I

4. A pump fluid control system for bypassing the output of at least one controlled pump in a series of at least two parallel pumps, said pumps normally discharging to a common outlet which comprises: a bypass pathway, said bypass pathway open to the output of the controlled pump, said bypass pathway being effective to provide a low pressure bypass for the output of the controlled pump other than through the normal outlet, said bypass pathway controlled by a valve effective to open and close the pathway, said valve having means for balancing the pressure acting on opposite sides of a valve member, a valve control means having means for unbalancing the pressures acting on the valve member and having means for sensing pressures from at least three areas of a fluid flow system which supplies fluid to the pumps and received the discharge from the pumps, said means for unbalancing being actuated in response to the pressures sensed at the three areas.

5. A pump fluid control system comprising: a fluid flow system having an inlet and an outlet, at least two parallel pumps interposed between said inlet and said outlet working on fluid passing through said fluid flow system, a control system for bypassing the output of at least one of said pumps whereby the output of that pump is not discharged to the outlet when said system is open and whereby the output from that pump is discharged to the outlet when said system is closed, said control system including a bypass pathway, a valve having an enclosure disposed in said pathway and having a valve member coacting with a valve seat to control flow through said pathway, said valve having means for balancing the pressure acting on opposite sides of the valve-member, means for bleeding pressure acting on one side of said valve member, means for sensing pressures from at least three areas of said fluid flow system and valve means for controlling said'bleed means in response to the pressures sensed by said sensing means.

6. In an aircraft fuel supply system having an inlet from a fuel source and an outlet to a fuel utilizer, the system having a variable speed booster pump open to the inlet and at least two constant speed pumps acting in parallel on the fuel within the system fed by the booster pump and discharging to the outlet, the improvement of means to bypass the output of at least one of said constant speed pumps, said means including a bypass pathway receiving at least a portion of the output of said one of said constant speed pumps, said pathway discharging to an area upstream of said constant speed pumps, valve means for controlling flow through said pathway, said valve means having means for balancing the fluid pressure acting on opposite sides of a valve member so that the valve. means normally closes said pathway, control system for said valve means including means for unbalancing one side of said valve member so that the valve means opens said pathway said unbalancing means being actuated in response to pressure differentials between fuel pressures sensed from at least three separate areas intermediate the inlet and outlet of said supply system.

7. A supply system of claim 6 wherein the pressure differentials indicate the speed of said booster pump and the operating condition of at least one of the nonbypassed constant speed pumps.

8. A supply system of claim 7 wherein the pressure differentials indicate the fuel utilization rate of the system as a function of fuel flow through the fuel supply system.

9. A system of claim 7 wherein booster pump speed is indicated as a function of pressure differential between the inlet to the booster pump and the outlet therefrom.

10. A system of claim 8 wherein fuel flow is determined as a function of pressure drop across a restricchamber.

14. A system according to claim 13, wherein said unbalancing means includes a drainage path connected to said enclosure and a plurality of pressure responsive members controlling flow in said drainage path.

15. A system of claim 14 wherein at least one of the said pressure responsive members is an axially movable spool valve interposed in said drainage path for the said enclosed chamber, the spool valve axially movable from open to closed positions in response to pressures acting on the axial ends of the spool valve.

Claims

1. A pump fluid control system comprising: a fluid pumping system including an inlet for receiving fluid, a booster pump in communication with said inlet and having an outlet in communication with an interstage, a main pump and at least one other pump connected in parallel between said interstage system, a control means for said pumping system for selectively diverting the main pump discharge to a bypass pathway and thereby remove the main pump Discharge from the flow to the common outlet, said control means including a valve means for controlling flow in the bypass pathway, said valve means including means for balancing the pressure acting on opposite side of a valve member thereof, said control means including means for sensing only fluid pressure from at least three different areas of said pump system and means for unbalancing the pressure as one side of the valve member in response to the pressures sensed by said sensing means so that unbalancing the pressures as the valve member of the valve means causes the valve means to open and provide a low pressure bypass for the main pump.

3. A pump fluid control system according to claim 2, wherein said second valve means includes at least one spool valve which is axially shifted between an opened and closed position in response to pressure acting on an axial end thereof.

5. A pump fluid control system comprising: a fluid flow system having an inlet and an outlet, at least two parallel pumps interposed between said inlet and said outlet working on fluid passing through said fluid flow system, a control system for bypassing the output of at least one of said pumps whereby the output of that pump is not discharged to the outlet when said system is open and whereby the output from that pump is discharged to the outlet when said system is closed, said control system including a bypass pathway, a valve having an enclosure disposed in said pathway and having a valve member coacting with a valve seat to control flow through said pathway, said valve having means for balancing the pressure acting on opposite sides of the valve member, means for bleeding pressure acting on one side of said valve member, means for sensing pressures from at least three areas of said fluid flow system and valve means for controlling said bleed means in response to the pressures sensed by said sensing means.

6. In an aircraft fuel supply system having an inlet from a fuel source and an outlet to a fuel utilizer, the system having a variable speed booster pump open to the inlet and at least two constant speed pumps acting in parallel on the fuel within the system fed by the booster pump and discharging to the outlet, the improvement of means to bypass the output of at least one of said constant speed pumps, said means including a bypass pathway receiving at least a portion of the output of said one of said constant speed pumps, said pathway discharging to an area upstream of said constant speed pumps, valve means for controlling flow through said pathway, said valve means having means for balancing the fluid pressure acting on opposite sides of a valve member so That the valve means normally closes said pathway, control system for said valve means including means for unbalancing one side of said valve member so that the valve means opens said pathway said unbalancing means being actuated in response to pressure differentials between fuel pressures sensed from at least three separate areas intermediate the inlet and outlet of said supply system.

7. A supply system of claim 6 wherein the pressure differentials indicate the speed of said booster pump and the operating condition of at least one of the non-bypassed constant speed pumps.

10. A system of claim 8 wherein fuel flow is determined as a function of pressure drop across a restriction intermediate the booster pump and the constant speed pumps.

11. A system of claim 7 wherein the operation of the non-controlled pump is determined as a function of pressure differential across the non-controlled pump.

12. A system of claim 7 wherein the operation of the non-controlled pump is determined as a function of pressure drop across a restriction in a conduit supplying fuel only to the non-controlled pump.

13. A system according to claim 6, wherein said balancing means comprises an orifice extending through the valve member, which is received in an enclosed chamber.