Gas turbine engine fuel system metering valve

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.

BACKGROUND

This disclosure relates to a metering valve for a fuel metering system.

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.

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

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.

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.

DETAILED DESCRIPTION

A highly schematic view of a fuel system10for a gas turbine engine30is shown inFIG. 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 system10are labeled with the prefix “P.”

The system10includes a pump14that pumps fuel from a tank12. Fuel from the pump14flows through the main filter18to the metering valve (MV)26and the pressure regulating valve (PRV)28. The pump14also supplies fuel PFA to fueldraulic actuators21and the servo pressure regulator (SPRV)24.

Upstream fuel P1from the pump14is provided to a metering valve (MV)26. The MV26is 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)24that is responsive to the main gear pump inlet fuel PGI and pump outlet fuel PFA. The modulated pressure PM is from a servo valve22that responds to FADEC commands for positioning the MV26. The MV26produces a downstream pressure P2that is provided to the engine combustor. The PRV28is also responsive to the upstream fuel P1via port44and downstream fuel pressure P2via port42to 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 BDVC32is also responsive to the pressure regulator fuel PR, the PBDCV signal from the MV and PGI.

The ports and their respective flow directions are shown inFIGS. 2A and 2B. A FADEC39is in communication with the MV26through a servo valve22which positions the MV using the modulated pressure PM. The FADEC also receives MV position information through an LVDT connected to the MV.

The MV26includes a housing34, which contains various fuel lines, schematically depicted inFIG. 1. A sleeve36is received in the housing34and sealed relative thereto by seals, such as O-rings, to fluidly separate the fuel inlets and outlets provided in the housing34. A spool38is slidably received within the sleeve36and is responsive to fuel pressures acting on the spool38to selectively communicate fuel to various components within the system10. To this end, the spool38includes first, second and third seal lands56,58,60. The first and third seal lands56,60selectively block and unblock some of the ports40-54.

Referring toFIG. 3A, the sleeve36includes a first P1port selectively in fluid communication with the first P2port42. In particular, the first seal land56selectively fluidly connects the first P1port through the annular space between the first and second seal lands56,58when the first seal land56moves 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 D1, first W1and position L1of the first seal land56relative to the left end of the spool38. In the example, the ratio L1/W1is 1.40-1.50, and for example, 1.44; the ratio W1/D1is 0.58-0.68, and for example, 0.63.

The second P2port46is fluidly connected to the first P2port42through housing plumbing lines.

The first P2port42includes two windows having a total area of 0.261 inch2(0.66 cm2) with axially elongated portions that permits a gradual flow (as the spool38moves from right to left in the figure) before becoming fully opened, as graphically depicted inFIG. 6A. The first P1port40includes four windows that are generally rectangular in shape to maximize flow through the port during the entire opening stroke of the spool38. The first P1port40includes a total area of 1.712 inch2(4.35 cm2).

Referring toFIG. 3B, the second P2port46and the PGI port48are fluidly connected (with the spool38all the way to the right in the figure) and the first P2port42fully blocked. In this position, the BDCV port50is blocked by the third seal land60. The third seal land60is at a second position L2from the left end and includes a second width W2and a second diameter D2. The ratio of D2/W2is 6.32-6.42, and for example, 6.37; the ratio of W2/D2is 0.95-1.10, and for example 1.05. The timing of the fluid connection and change in flow regulating area between the second P2port46and the PGI port48is graphically shown inFIG. 6B.

Referring toFIGS. 5A and 5B, the PR port52and the BDCV port50are fluidly connected with the spool38to the left. The BDCV port50is rectangular in shape to maximize flow through the port. The total area of the BDCV port50is less than the total area of the PR port52. The timing of the fluid connection and change in flow regulating area between the PR port52and the BDCV port50is graphically shown inFIG. 6C.

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.