Abstract:
A metering valve for a gas turbine engine fuel system includes a sleeve including first, second, third, fourth, fifth and sixth ports respectively axially spaced apart from one another. A spool is slidably received in the sleeve and includes first, second and third seal lands. The first seal land selectively connects the first and second ports to one another, and the third seal land selectively connects the third and fourth ports to one another and the fifth and sixth ports to one another.

Description:
BACKGROUND 
       [0001]    This disclosure relates to a metering valve for a fuel metering system. 
         [0002]    Gas turbine engines are known, and typically include a compressor compressing air and delivering it to a combustor. The compressed air is mixed with fuel in the combustor, combusted, and the products of combustion pass downstream over turbine rotors, driving the rotors to create power. 
         [0003]    The metering valve provides metered flow to the combustor, provides position feedback to the full authority digital engine controller (FADEC), moves in response to a FADEC command, shuts fuel flow off in response to a FADEC command and provides pressure signals to various fuel system components. 
       SUMMARY 
       [0004]    In one exemplary embodiment, a metering valve for a gas turbine engine fuel system includes a sleeve including first, second, third, fourth, fifth and sixth ports respectively axially spaced apart from one another. A spool is slidably received in the sleeve and includes first, second and third seal lands. The first seal land selectively connects the first and second ports to one another, and the third seal land selectively connects the third and fourth ports to one another and the fifth and sixth ports to one another. 
         [0005]    In another exemplary embodiment, a fuel system for a gas turbine engine includes a pump configured to pump fuel from a tank. A metering valve is fluidly connected to and arranged downstream from the pump. The metering valve includes a sleeve including first, second, third, fourth, fifth and sixth ports respectively axially spaced apart from one another. A spool is slidably received in the sleeve and includes first, second and third seal lands. The first seal land selectively connects the first and second ports to one another, and the third seal land selectively connects the third and fourth ports to one another and the fifth and sixth ports to one another. The first and fourth ports are fluidly connected to one another irrespective of spool position. The second port is fluidly connected to and downstream from the pump. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The disclosure can be further understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
           [0007]      FIG. 1  is a schematic of a portion of a fuel system for a gas turbine engine. 
           [0008]      FIG. 2A  is a cross-sectional view of a metering valve with a housing, sleeve and spool. 
           [0009]      FIG. 2B  is a perspective view of the sleeve illustrating various ports. 
           [0010]      FIG. 3A  is a cross-sectional view of the metering valve with the spool in a position permitting partial flow through a P 2  port in the sleeve. 
           [0011]      FIG. 3B  is a cross-sectional perspective view of the metering valve with the spool in a position permitting flow through a P 2  port in the sleeve to a PGI port. 
           [0012]      FIG. 4A  is a cross-sectional view of the metering valve with the spool in the position fully blocking flow through the P 2  port. 
           [0013]      FIG. 4B  is a cross-sectional view of the metering valve with the spool in the position permitting full flow through the P 2  port. 
           [0014]      FIG. 5A  is a cross-sectional perspective view of the metering valve with the spool in a position permitting flow through a PR port in the sleeve to a BDCV port. 
           [0015]      FIG. 5B  is an enlarged cross-sectional perspective view of the metering valve illustrating the unblocked BDCV port. 
           [0016]      FIG. 6  graphically depicts the flow regulating area of various ports at particular spool positions; graph A depicts the flow regulating area connecting the P 1  and P 2  ports; graph B depicts the flow regulating area connecting the P 2  and PGI ports; graph C depicts the flow regulating area connecting the PR and BDCV ports. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    A highly schematic view of a fuel system  10  for a gas turbine engine  30  is shown in  FIG. 1 . It should be understood that various fluid connections and components are omitted from the schematic for clarity. The fuel flowing in the various lines within the system  10  are labeled with the prefix “P.” 
         [0018]    The system  10  includes a main pump  14  that pumps fuel from a tank  12 . Fuel from the pump  16  flows through the main filter  18  to the metering valve (MV)  26  and the pressure regulating valve (PRV)  28 . The pump  14  also supplies fuel PFA to fueldraulic actuators  21  and the servo pressure regulator (SPRV)  24 . 
         [0019]    Upstream fuel P 1  from the pump  14  is provided to a metering valve (MV)  26 . The MV  26  is responsive to main gear pump inlet fuel PGI, SPRV regulated pressure fuel PR, and a modulated pressure PM. The regulated pressure fuel PR is provided by a servo pressure regulator (SPR)  24  that is responsive to the main gear pump inlet fuel PGI and pump outlet fuel PFA. The modulated pressure PM is from a servo valve  22  that responds to FADEC commands for positioning the MV  26 . The MV  26  produces a downstream pressure P 2  that is provided to the engine combustor. The PRV  28  is also responsive to the upstream fuel P 1  via port  44  and downstream fuel pressure P 2  via port  42  to produce a bypass flow, discharge pressure fuel PDI. This bypass flow is sent to a bypass directional control valve (BDCV)  32 , which sends the bypass flow back to one of two possible low pressure locations upstream of the pump, depending on the state of the BDCV. The BDVC  32  is also responsive to the pressure regulator fuel PR, the PBDCV signal from the MV and PGI. 
         [0020]    The ports and their respective flow directions are shown in  FIGS. 2A and 2B . A FADEC  39  is in communication with the MV  26  through a servo valve  22  which positions the MV using the modulated pressure PM. The FADEC also receives MV position information through an LVDT connected to the MV. 
         [0021]    The MV  26  includes a housing  34 , which contains various fuel lines, schematically depicted in  FIG. 1 . A sleeve  36  is received in the housing  34  and sealed relative thereto by seals, such as O-rings, to fluidly separate the fuel inlets and outlets provided in the housing  34 . A spool  38  is slidably received within the sleeve  36  and is responsive to fuel pressures acting on the spool  38  to selectively communicate fuel to various components within the system  10 . To this end, the spool  38  includes first, second and third seal lands  56 ,  58 ,  60 . The first and third seal lands  56 ,  60  selectively block and unblock some of the ports  40 - 54 . 
         [0022]    Referring to  FIG. 3A , the sleeve  36  includes a first P 1  port selectively in fluid communication with the first P 2  port  42 . In particular, the first seal land  56  selectively fluidly connects the first P 1  port through the annular space between the first and second seal lands  56 ,  58  when the first seal land  56  moves from the fully blocked position ( FIG. 4A ) to the fully open position ( FIG. 4B ). The timing of this event is determined in part by the first diameter D 1 , first W 1  and position L 1  of the first seal land  56  relative to the left end of the spool  38 . In the example, the ratio L 1 /W 1  is 1.40-1.50, and for example, 1.44; the ratio W 1 /D 1  is 0.58-0.68, and for example, 0.63. 
         [0023]    The second P 2  port  46  is fluidly connected to the first P 2  port  42  through housing plumbing lines. 
         [0024]    The first P 2  port  42  includes two windows having a total area of 0.261 inch 2  (0.66 cm 2 ) with axially elongated portions that permits a gradual flow (as the spool  38  moves from right to left in the figure) before becoming fully opened, as graphically depicted in  FIG. 6A . The first P 1  port  40  includes four windows that are generally rectangular in shape to maximize flow through the port during the entire opening stroke of the spool  38 . The first P 1  port  40  includes a total area of 1.712 inch 2  (4.35 cm 2 ). 
         [0025]    Referring to  FIG. 3B , the second P 2  port  46  and the PGI port  48  are fluidly connected (with the spool  38  all the way to the right in the figure) and the first P 2  port  42  fully blocked. In this position, the BDCV port  50  is blocked by the third seal land  60 . The third seal land  60  is at a second position L 2  from the left end and includes a second width W 2  and a second diameter D 2 . The ratio of D 2 /W 2  is 6.32-6.42, and for example, 6.37; the ratio of W 2 /D 2  is 0.95-1.10, and for example 1.05. The timing of the fluid connection and change in flow regulating area between the second P 2  port  46  and the PGI port  48  is graphically shown in  FIG. 6B . 
         [0026]    Referring to  FIGS. 5A and 5B , the PR port  52  and the BDCV port  50  are fluidly connected with the spool  38  to the left. The BDCV port  50  is rectangular in shape to maximize flow through the port. The total area of the BDCV port  50  is less than the total area of the PR port  52 . The timing of the fluid connection and change in flow regulating area between the PR port  52  and the BDCV port  50  is graphically shown in  FIG. 6C . 
         [0027]    Although an example embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of the claims. For example, part areas may be within +/−5% of the specified areas. For that reason, the following claims should be studied to determine their true scope and content.