Abstract:
A fuel control system for supplying metered quantities of fuel from a fuel supply ( 11 ), through a fuel pump ( 13 ), a metering valve ( 15 ) and a pressurizing valve ( 17 ) to a plurality of engine fuel manifolds ( 31   a   , 31   b,    33 ) includes an ecology valve ( 43 ) for withdrawing fuel from the engine fuel manifolds ( 31   a   , 31   b   , 33 ) during cessation of engine operation and for returning fuel to the engine fuel manifolds ( 31   a   , 31   b   , 33 ) to be burned during normal engine operation. The ecology valve ( 43 ) includes a valve housing ( 44 ) having a plurality of ecology ports ( 50, 52, 54 ) adapted to be coupled to corresponding ones of the engine fuel manifolds ( 31   a   , 31   b,    33 ) and a control port ( 46 ) adapted to be connected to a corresponding control port ( 45 ) of the fuel pressurizing valve ( 17 ). A movable piston ( 63 ) is supported within the valve housing ( 44 ) for reciprocable motion and divides the interior of the valve housing ( 44 ) into a variable volume control chamber ( 71 ) coupled to the control port ( 46 ) and a variable volume fuel reservoir ( 55 ) which is selectively coupled to and uncoupled from the ecology ports ( 50, 52, 54 ) by the piston ( 63 ). Fuel is withdrawn from the manifolds ( 31   a   , 31   b,    33 ) seriatim. A fuel flow dividing arrangement is located intermediate the pressurizing valve ( 17 ) and the engine fuel manifolds ( 31   a   , 31   b   , 33 ) for distributing appropriately fuel flow among the manifolds and includes a concatenated pair of two-way splitter valves ( 39, 41 ) comprising a first splitter valve ( 39 ) distributing the fuel flow between an atomizer nozzle manifold ( 31   b ) and the remaining manifolds ( 31   a   , 33 ), and a second splitter valve ( 41 ) distributing down stream fuel flow from the first splitter valve ( 39 ) between upper and lower manifolds ( 31, 33 ).

Description:
This is a division of patent application Ser. No. 09/361,932 filed Jul. 27, 1999. 
    
    
     The present invention relates generally to fuel delivery systems for engines, especially aircraft gas turbine engines, and more particularly to ecology and fuel flow splitting functions for such fuel delivery systems. 
     Some fuel delivery systems for gas turbine engines require multiple fuel manifolds to segregate various types of fuel nozzles for optimal engine performance. A means of dividing this flow between the manifolds is therefor required. U.S. Pat. No. 5,809,771 Wernberg discloses an ecology valve and a fuel flow splitting valve having a single piston operable in two different regions, one for modulating flow to primary and secondary engine nozzles as a function of fuel pressure and another where flow to primary and secondary engine nozzles is determined by the fixed port geometry. It is very difficult to extend this concept to more than two distinct engine manifolds. 
     Some engines also require an ecology function that removes a set quantity of fuel from the engine fuel manifold(s) upon cessation of engine operation. Fuel removal is required for two reasons. First, it keeps fuel from vaporizing into the atmosphere. Second, it keeps fuel from coking on the engine&#39;s fuel nozzles, a condition that hinders nozzle performance. Prior art ecology systems have used an arrangement of pistons, check valves, plumbing, reservoirs and pumps to accomplish this task. In engines requiring multiple fuel manifolds, multiple ecology valves or a multiple chambered ecology valve have been used. These types of architecture result in complex, high cost and weight ecology systems. A two chambered valve is disclosed in the above-mentioned Wernberg U.S. Pat. No. 5,809,771. In the Wernberg system, fuel is simultaneously withdrawn from the two manifolds and a separate chamber is required for each engine manifold to ensure discrete fuel removal from those manifolds upon engine shut-down. It is also very difficult to extend this concept to more than two distinct engine manifolds. The Wernberg system employs at least one check valve downstream of the ecology valve for diverting a part of the modulated flow from the primary to the secondary manifold. Such downstream valving allows a degree of undesirable cross-talk between the manifold supply lines and may reduce engine fuel flow reliability or increase the load on the fuel supply pump. 
     It is desirable to minimize the fuel remaining in an engine fuel manifold upon cessation of engine operation and to provide a compact, economical ecology function for fuel supply systems. It is also desirable to achieve such an ecology function by employing a simple single diameter piston valve which is controlled solely by a signal from a pressurizing valve, and to accomplish the ecology function while avoiding any cross-talk between the several manifold fuel supply lines thereby maintaining the fuel pressure integrity in those several lines. It is further desirable to avoid this cross-talk while achieving a fuel splitting function which is operable to appropriately distribute fuel to a plurality of engine fuel manifolds. 
     The present invention provides solutions to the above problems in the form of a fuel divider and ecology system adapted for an engine requiring three discrete fuel manifolds. One manifold contains atomizer nozzles (for engine start), and two manifolds contain air blast nozzles, one servicing the lower half and the other servicing the upper half of the engine. For the flow dividing function, the system incorporates a plurality of valves to appropriately distribute metered burn flow to these three fuel manifolds. This system accomplishes the ecology function using one single chamber staged valve, and modifying the main fuel control pressurizing valve to include a pressure switching function. This approach limits the ecology components to one ecology valve piston, and one plumbed line from the pressurizing valve to control it. The fuel splitting function is achieved by a first splitter valve which divides the fuel flow from a pressurizing valve between atomizer or start-up nozzles and air blast or main running nozzles; and a second splitter valve which subdivides flow between the upper and lower manifolds. 
     In accordance with one form the invention, an ecology valve for minimizing the accumulation of fuel in a multiple fuel manifold engine system when the engine is shut down has a control port coupled to and controlled solely by an engine fuel system pressurizing valve and a housing with a piston reciprocable therein between first and second extreme positions. The piston defines, in conjunction with the housing, a variable volume chamber for sequentially withdrawing fuel from each of the engine fuel manifolds when the engine is de-energized and the piston moves from the first extreme position toward the second extreme position thereby purging the manifolds of fuel. There is a spring within the housing which supplies a force to the piston to urge the piston toward the second extreme position and the piston responds to high pressure at the ecology valve control port overpowering the spring to move toward the first extreme position. There are a plurality of sidewall or ecology ports in the housing selectively opened and closed by piston movement to couple the variable volume chamber and selected fuel manifolds. 
     In accordance with another form of the invention, an improved fuel flow dividing arrangement is located intermediate a pressurizing valve and a plurality of engine fuel manifolds for appropriately distributing fuel flow among the manifolds. The arrangement includes a concatenated pair of two-way splitter valves one of which distributes fuel flow between an atomizer nozzle manifold and the remaining manifolds. Another splitter valve distributes the down stream fuel flow from the first splitter valve between upper and lower air blast nozzle manifolds. The second splitter valve provides a pair of low volume fuel flow paths to the upper and lower manifolds during engine start-up and a second pair of high volume fuel flow paths to the upper and lower manifolds during normal engine running conditions. There is a head effect fuel flow restricting valve in the low volume fuel flow path to the lower manifold to compensate for elevation difference induced low burn rate fuel flow differences between the upper and lower manifolds. The first splitter valve provides a low volume fuel flow path to the second splitter valve during engine start-up and a second high volume fuel flow path to the second splitter valve during normal engine running conditions, and switches fuel routed to the atomizer nozzles from pressurizing valve discharge pressure to the lower manifold pressure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a schematic representation of an illustrative aircraft fuel system including an ecology function according to the present invention; 
     FIG. 2 is a detailed cross-sectional view of the pressurizing valve, and flow divider and ecology module of FIG. 1 in the engine off position; 
     FIG. 3 is a cross-sectional view similar to FIG. 2, and illustrating the pressurizing valve beginning to open prior to engine start-up and commencement of fuel discharge from the ecology valve; 
     FIG. 4 is a cross-sectional view similar to FIGS. 2 and 3, and illustrating a second stage of fuel discharge from the ecology valve; 
     FIG. 5 is a cross-sectional view similar to FIGS. 2-4, and illustrating a third stage of fuel discharge from the ecology valve; 
     FIG. 6 is a cross-sectional view similar to FIGS. 2-5, and illustrating start-up conditions for the splitter valves; 
     FIG. 7 is a cross-sectional view similar to FIGS. 2-6, and illustrating the flow divider and ecology module in the normal engine run configuration; and 
     FIG. 8 is a cross-sectional view similar to FIGS. 2-7 but illustrating an alternative embodiment of the head effect valve of the flow divider and ecology module during normal engine run configuration. 
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views of the drawing. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following abbreviations are used for various pressures throughout the description: 
     PIN fuel control inlet pressure 
     POF pump interstage pressure before filter 
     PO pump interstage pressure after filter 
     P 1  high pressure pump discharge 
     P 2  metering valve discharge pressure 
     P 3  pressurizing valve discharge pressure 
     PAT burn flow pressure to atomizer nozzles 
     PAB burn flow pressure to air blast nozzles 
     PABL burn flow pressure to lower air blast nozzles 
     PABU burn flow pressure to upper air blast nozzles 
     PXE ecology valve control pressure 
     FIG. 1 is a block diagram showing a gas turbine engine fuel divider and ecology module, as well as the related upstream and down stream fuel system components. In FIG. 1, an illustrative aircraft fuel supply system includes a supply tank  11  from which fuel is fed to boost pump  13  and a filter  21  to a high pressure pump  14 . The high pressure pump  14  discharge pressure P 1  is supplied to a variable orifice metering valve  15  and through a pressurizing valve  17  and a flow divider and ecology module  19  to an engine. The pressurizing valve  17  maintains a reference pressure level P 2  on the downstream side  24  of the metering valve  15  and the bypass valve  23  selectively diverts fuel from line  25  back through line  27  to the high pressure pump  14  inlet to maintain a constant head or pressure drop across the metering valve  15 . Fuel entering the fuel manifolds  31  and  33  of the engine from pressurizing valve  17  flows through line  37 , a first flow dividing valve  39  and a second flow dividing valve  41 . Fuel entering the atomizer nozzles in fuel manifolds  31  from pressurizing valve  17  flows directly from the first flow divider valve  39  to the engine manifold. The pressurizing valve  17  opens when burn flow pressure is sufficiently greater than return flow pressure, that is, when the pressure differential between P 2  on line  24  and P 0  on line  51  becomes sufficiently great and closes when that pressure differential drops below a certain threshold. The pressurizing valve  17  includes appropriate lands and grooves to couple selectively the staged ecology valve  43 , by means of control line or port  45 , to either fuel control inlet pressure on line  47  or to metering valve  15  discharge pressure by way of line  24 . The components of the flow divider and ecology module  19  are shown in greater detail in FIGS. 2-7. 
     In FIGS. 2-7, the ecology valve  43  includes a valve housing  44  including ecology ports  50 ,  52  and  54  which are coupled to the engine fuel manifolds  31 and  33 . The ecology valve also includes a control port  46  connected to a corresponding control port of the fuel pressurizing valve  17 . There is a movable piston  63  supported within the valve housing  44  for reciprocable motion along an axis. The piston  63  divides the valve housing into a variable volume control chamber  71  (see FIG. 3) which is coupled to the control port  46  and a variable volume fuel reservoir  55 . The piston  133  has one extreme position (FIGS. 5,  6  and  7 ) in which a sidewall port  64  is open to a first port  54  to couple the fuel reservoir  55  to a first or upper engine fuel manifold  33  while the remaining ports  52  and  50  are closed isolating the reservoir from the lower engine fuel manifold  31  which comprises air blast manifold  31   a  and atomizer manifold  31   b . The piston  63  has a second extreme position (FIG. 2) in which a second port  50  is open to couple the fuel reservoir  55  to the hybrid nozzles of the atomizer manifold  31   b  of the second or lower engine fuel manifolds  31  while the other ports  52  and  54  are closed isolating the reservoir from air blast manifold  31   a  of lower manifolds  31  and from the remaining engine fuel upper manifold  33 . In a preferred form, there are exactly three ports selectively opened and closed by piston motion with the port  52  opening to couple the fuel reservoir to engine fuel lower manifolds  31  only while the piston is in transition and closing both of the other ports  50  and  54  as in the transition from FIG. 3 to FIG.  4 . Thus, the piston  63  has one extreme position (FIGS. 5-7) in which it closes at least one port such as  50  and a second extreme position (FIG. 2) in which it closes at least one other port  54 . Fuel is withdrawn sequentially from the manifolds  33 ,  31   a  and  31   b . There are three manifolds ( 31   a ,  31   b  and  33 ) and three disjoint time intervals, one for each manifold, during which fuel is withdrawn from or supplied to exactly one manifold. Both withdrawing from and supplying fuel to any one manifold is substantially completed before the withdrawal from or supplying to another manifold commences. 
     FIG. 2 shows the pressurizing valve  17  closed, blocking the P 2 /P 3  flow path, with its switching function connecting PXE pressure on line  45  (FIG. 1) to PIN pressure on line  47  by way of the groove  59  in piston  57 . As illustrated in FIG. 2, this low pressure PIN at the ecology valve control port  46  exerts a force on the piston  63  which is less than the force exerted by spring  48  to urge the piston  63  toward its uppermost position as illustrated, a condition indicative of a quiescent engine condition. The ecology valve  43  is thereby shown filled with fuel and the engine manifolds are purged. Set amounts of fuel have been retracted from the manifolds into the spring cavity  55  of the valve. The flow divider valves  39  and  41 , and head effect valve  53  are also in their closed positions. These are the engine off positions of all valves. 
     FIG. 3 shows the piston  57  of pressurizing valve  17  at the P 2 /P 3  near open or cracking position, with its switching function connecting PXE pressure in line  45  to P 2  pressure in passage  49  via groove  61 . At this position with the P 2 /P 3  flow path blocked, fuel control pressurization is up, and manifold pressure (as well as the spring side of the ecology valve) is down. The piston  63  of ecology valve  43  is shown traveling toward its energized position, staging the return of stored fuel from chamber  55  on the spring side of the valve to the manifolds. At this ecology valve stage, fuel has been returned from chamber  55  to the atomizer manifold  31   b  (PAT pressure) by way of line  65 . This process is occurring during engine spool up (prior to start). 
     FIG. 4 shows the second stage position of the ecology valve  43 , where fuel has been returned by way of conduit  67  to the lower air blast fuel manifolds  31  (PABL pressure). The pressurizing valve  17  and flow divider valves  39  and  41  remain in the same functional positions as described in FIG.  3 . 
     FIG. 5 shows the final position (last stage) of the ecology valve  43 , where fuel has been returned to the upper air blast fuel manifold  33  (PABU pressure) through conduit  69 . The pressurizing valve  17  and flow divider valves  39  and  41  remain in the same functional positions as described in FIGS. 3 and 4 up to the time that the ecology valve  43  reaches its hard stop, fully energized position with the chamber  71  (at pressure PXE) at its maximum volume. It should be noted that all three manifolds  31   a ,  31   b  and  33  have been refilled by the volume of fuel expelled from the ecology valve chamber  55 . 
     Comparing FIGS. 2-5 it will be noted that the piston  63  has the single sidewall port  64  which sequentially communicates with housing  44  sidewall ports  50 ,  52  and  54 . Thus, the ecology valve  43  has a first sidewall port  50  which is closed by the piston  63  when the piston is in its lowermost (FIG. 5) extreme position, a second sidewall port  52  which is closed by the piston  63  when the piston is in lowermost (FIG. 5) as well as its uppermost (FIG. 2) extreme positions, and a third sidewall port  54  which is closed by the piston  63  when the piston is in its uppermost extreme position. The second or middle sidewall port  52  opens during piston movement between its extreme positions to couple the variable volume chamber  55  with engine fuel lower manifolds  31 . While there may be piston positions such as illustrated in FIG. 4 where the port  64  momentarily communicates with two sidewall ports,  52  and  54  for example, in substantially all piston positions, the piston closes at least two sidewall ports. All three ports are never open simultaneously. 
     FIG. 6 shows the pressurizing valve  17  opened, allowing metered fuel flow to pass to the flow divider and ecology module  19  (FDEM) through conduit  37 . As flow enters the FDEM  19 , the piston  75  of atomizer/air blast flow divider valve  39  translates off its soft seat  74 , allowing fuel to flow to the atomizer manifold  31   b  at PAT pressure through line  73  and restricted flow to pass through port  83  and line  42  to the upper/lower air blast manifold flow divider valve  41  (PAB pressure) via sequential side wall orifices  77  and  78  in piston  75 . The piston  79  of upper/lower air blast manifold flow divider valve  41  translates from its closed position, allowing flow to the upper manifold  33  through conduits  81  and  69  at PABU pressure. The translation of piston  79  also allows a biased flow of fuel to the lower manifold  31  (PABL pressure) through head effect valve  53  and line  67 . The PABL pressure flow is biased by the head effect valve  53  which compensates for differences in elevation and line loss between the upper and lower manifolds. Without this compensation, the lower manifolds  31   a  and  31   b  would flow more fuel than the upper manifold  33 , particularly at low metered burn flow rates. FIG. 6 illustrates the approximate positions of the valves during an engine start up. 
     FIG. 7 shows the conditions defined in FIG. 6, but with a higher rate of burn flow. As flow increases, the pressurizing valve  17  further opens allowing additional metered fuel flow to the FDEM  19  through line  37 . The piston  75  of atomizer/air blast flow divider valve  39  further translates from its closed position, opening port  83  that allows additional fuel flow to pass to the upper/lower air blast manifold flow divider valve  41  (PAB pressure) to increase the flow that was previously through side wall orifices  77  and  78  in piston  75 . The side wall orifices  77  and  78  are staged so that when orifice  77  is closing, the second orifice  78  opens, keeping the orifice area and flow from diminishing. At this position of valve  75 , fuel routed to the combination atomizer and air blast nozzles (hybrid nozzles) of atomizer manifold  31   b  is supplied from the lower manifold pressure (PABL) via lines  76  and  73  and valve  39  opening  80 , rather than from pressurizing valve  17  discharge pressure P 3 . The purpose for providing lower air blast manifold pressure (PABL) to the atomizer manifold  31   b  is to equate the total flow of a hybrid nozzle in manifold  31   b  to that of the flow of an air blast nozzle in the air blast manifold  31   a  (see FIG.  1 ). The piston  79  of upper/lower air blast manifold flow divider valve  41  further translates from its closed position, opening ports  85  that allow additional fuel flow to the upper (PABU pressure) manifold  33  and the lower (PABL pressure) manifolds  31 , while maintaining equal flow to these manifolds. 
     Comparing FIGS. 6 and 7, the splitter valve  39  provides a low volume fuel flow path by way of side wall orifices  77  and  78  to the splitter valve  41  during engine start-up and a second high volume fuel flow path via port  83  (in parallel and in addition to the first) to the splitter valve  41  during normal engine running conditions. As also seen comparing FIGS. 6 and 7, the splitter valve  41  provides a pair of low volume fuel flow paths by way of passage  81  and head effect valve  53  to the upper manifold  33  and lower manifolds  31  respectively during engine start-up and a second pair of high volume fuel flow paths  69  and  67  to the upper manifold  33  and the lower manifolds  31  respectively during normal engine running conditions. The head effect fuel flow restricting valve  53  is in the low volume fuel flow path to the manifolds  31  to compensate for elevation difference, induced low burn rate fuel flow differences between the upper and lower manifolds. FIG. 7 illustrates the approximate positions of the valves for an engine run condition. It should be noted that during all engine operating conditions (FIGS.  6  and  7 ), the piston  63  of the ecology valve  43  is in its full energized position against that respective hard stop, making the ecology valve  19  a non-dynamic feature with respect to metered burn flow to the engine. 
     The process of cycling an engine from an engine-off condition, through start-up and substantially full throttle run, and subsequent shut-down and back to the engine-off condition should now be clear. When the pilot or other operator issues a command to start the engine, P 2  pressure is supplied by way of line  45  to expand chamber  71  and discharging a quantity of fuel from the ecology reservoir  55  by way of port  50  into manifold  31   b . Additional motion of piston  63  expels fuel into the other two manifolds  31   a ,  33  from reservoir  55 . Additional fuel is supplied to manifold  31   b  and a limited quantity of additional fuel from fuel source  11  is supplied to the manifolds  31   a  and  33  to start the engine. The supply of fuel to all manifolds is increased to bring the engine to substantially full throttle operation. Later, the pilot or other operator issues a shut-down command interrupting fuel flow to all the manifolds to initiate engine shut-down. Lines  45  and  47  are reconnected by the pressurizing valve  17  and piston  63  moves upward under the urging of spring  48  sequentially extracting fuel from the manifolds and storing the extracted fuel in the ecology reservoir  55  to be burned during a subsequent engine start-up. 
     FIG. 8 illustrates the aircraft fuel system of FIG. 7 but includes an alternative embodiment for the head effect valve  53  wherein weight or load member  92  and pressure loaded pin  91  are used to urge ball or valve member  93  against its seat. During normal engine run conditions, PAT and PABL pressures in lines  73  and  67  become equal as also shown in FIG. 7, with no pressure differential existing across the pin  91 . In this condition, the ball  93  is urged against its seat solely by the force exerted by the combined weight of the pin  91  and weight  92 , compensating only for head effect and line losses. During engine start-up conditions as illustrated in FIG. 6, PAT pressure in line  73   a  and its associated orifice (see FIG. 8) and which is exerted on the end of the pin  91  is greater than PABL pressure on the other end of the pin, which creates additional force to urge the ball valve  93  against its seat. This further throttles or lessens fuel flow being delivered to the lower manifold air blast nozzles via line  67 , which compensates for the greater flow being delivered to the lower manifold atomizer nozzles via line  73  during engine start-up. This results in equal flow to the upper and lower halves of the engine for all conditions, including engine start-up. It should be noted that the weight  92  shown in the head effect valve  90  of FIG. 8 could be replaced with a spring as shown in FIGS. 2-7, and the spring or weight shown in FIGS. 2-8 could be replaced by any other equivalent device or structure that provides an appropriate load upon the ball valve.