Patent Description:
Valves are used in any number of applications. In one application a metering valve is incorporated into a fuel supply system for supplying fuel to a combustor nozzle on a gas turbine engine.

EMIDS, such as electrohydraulic servo valves (EHSV) are also used in many applications. In one application an EHSV is incorporated to control hydraulic fluid flow to control the position of a metering valve.

There are a number of challenges with providing adequate fluid flow across such valve under different conditions.

<CIT> describes a dual pump/dual bypass fuel pumping system. <CIT> describes a high efficiency <NUM>-stage fuel pump and control scheme for gas turbines.

A fluid flow system is described herein and defined in claim <NUM>.

A fuel system for a gas turbine engine is also disclosed.

A fluid flow system <NUM> is illustrated in <FIG>. The fluid flow system <NUM> may be used to meter fuel to a nozzle <NUM> on an engine <NUM>, for example. The engine <NUM> may be a gas turbine engine, for example. Gas turbine engines are known, and may generally include a fan section, a compressor section, a combustor section and a turbine section, among other components. The nozzle <NUM> may be a nozzle <NUM> into a combustor section. The fluid flow system <NUM> may be utilized for applications other than fuel supply.

The fluid flow system <NUM> generally includes an electromechanical interface device (EMID) <NUM> and a metering valve <NUM>. The EMID <NUM> may be an electrohydraulic servo valve (EHSV), torque motor, or other device, for example. The EMID <NUM> and metering valve <NUM> control fluid to the nozzle <NUM> from a variable pressure source. A first fluid source <NUM> and a second fluid source <NUM> are in communication with the EMID <NUM> and then the metering valve <NUM>. In some examples, fluid from the first fluid source <NUM> also flows to the metering valve <NUM> to be delivered to nozzle <NUM>. In one example, the first fluid source <NUM> is a high-pressure fluid source and the second fluid source <NUM> is a low-pressure fluid source. In some examples, a pump <NUM>, <NUM> at each of the first and second fluid sources <NUM>, <NUM>, respectively, supplies the fluid to the system <NUM>. In this embodiment each source <NUM> and <NUM> are fuel.

In some examples, additional fluid flow lines <NUM>, <NUM> connect the first source <NUM> to the EMID <NUM> and the metering valve <NUM>. Fluid flow line <NUM> connects the first source <NUM> and the inlet port <NUM> of the metering valve <NUM>. Fluid flow line <NUM> connects the first source <NUM> and the EMID <NUM>. A fluid line <NUM> connects the metering valve <NUM> to the fuel nozzle <NUM>.

In this example, the EMID <NUM> is in fluid communication with the metering valve <NUM> via two fluid lines <NUM>, <NUM>. The EMID <NUM> modulates fluid from the high-pressure source <NUM> and the low-pressure source <NUM> to achieve a pressure differential to the metering valve <NUM>. An electronic control <NUM>, shown schematically, selectively controls the EHSV <NUM>.

The first fluid line <NUM> is in communication with a first chamber <NUM> at a first end <NUM> of the metering valve <NUM>. The second fluid line <NUM> is in communication with a second chamber <NUM> at a second end <NUM> of the metering valve <NUM>. The metering valve <NUM> also includes a spool <NUM> arranged between the first and second chambers <NUM>, <NUM>. An annulus <NUM> is defined about the spool <NUM>. The annulus <NUM> is in communication with an inlet port <NUM> and an outlet port <NUM>. A pressure difference between the first and second chambers <NUM>, <NUM> moves the spool <NUM>, which meters fluid between the inlet and outlet ports <NUM>, <NUM> by blocking portions of the inlet and/or outlet ports <NUM>, <NUM>. The speed at which the spool <NUM> moves based on the pressure differences between the chambers <NUM>, <NUM> is known as the slew rate.

Hydraulic control of a metering valve <NUM> through an EMID <NUM> is dependent upon the pressure within the system <NUM>. Thus, for a given fluid supply, the slew rate of the metering valve <NUM> will increase as the pressure differential between lines <NUM> and <NUM> is increased. The EHSV <NUM> controls the pressure acting on either end of the metering valve <NUM> to achieve a desired position for spool <NUM>.

As the pressure changes between the chambers <NUM>, <NUM> the slew rate may increase. It is undesirable for the slew rate to exceed a predetermined threshold. To prevent the pressure differences that cause a slew rate above the predetermined threshold, fixed orifices <NUM> and <NUM> may be arranged between the EMID <NUM> and the metering valve <NUM>.

In this example, a first fixed orifice <NUM> is arranged along the first fluid line <NUM> and a second fixed orifice <NUM> is arranged along the second fluid line <NUM>. The fixed orifices <NUM>, <NUM> are arranged between the EMID <NUM> and metering valve <NUM> to limit the flow rate of fuel to the metering valve <NUM>. The fixed rate orifices <NUM>, <NUM> are sized to maintain the flow of fluid within a predetermined pressure range. For example, there may be a predetermined threshold flow rate that is a maximum flow rate and the orifices <NUM>, <NUM> are sized to ensure the pressure difference between the first chamber <NUM> and the second chamber <NUM> remains below the predetermined threshold. This maintains the slew rate below the predetermined maximum.

While this application specifically discloses a metering valve in a fuel system, other valves for controlling fluid flow in other applications may benefit from the teachings of this disclosure.

<FIG> shows an example EMID <NUM>. In this example, the EMID <NUM> is an electrohydraulic servo valve (EHSV). The EHSV <NUM> has two stages including a torque motor <NUM> and a hydraulic mechanism <NUM> used to drive a spool <NUM> of a spool valve <NUM>. The torque motor <NUM> controls the flow of hydraulic fluid which drives the hydraulic mechanism <NUM> and the spool <NUM>. The torque motor <NUM> includes an armature <NUM> and magnetic coils <NUM>. The armature <NUM> is positioned by the magnetic force from the energized coils <NUM> to provide a supply pressure <NUM> to position the hydraulic mechanism <NUM>. The hydraulic mechanism <NUM> attached to the torque motor <NUM> may be a jet type, or any other type of hydraulic mechanism.

The spool <NUM> has a right spool valve land <NUM> and a left spool valve land <NUM> on a spool <NUM>. The right spool valve land <NUM> controls communication with the second fluid line <NUM> and the left spool valve land <NUM> controls communication with the first fluid line <NUM>. The spool <NUM> moves in response to fluid pressure in a left spool chamber <NUM> and a right spool chamber <NUM>. End lands <NUM> provide reaction surfaces for fluid in chambers <NUM> and <NUM>. Source <NUM> is directed into chambers between end lands <NUM> and each of lands <NUM> and <NUM>. Source <NUM> is directed into a chamber between lands <NUM> and <NUM>. Electronic control <NUM> positions spool <NUM> such that a desired mix from sources <NUM> and <NUM> passes into lines <NUM> and <NUM>, to in turn achieve a desired position of the spool <NUM> in metering valve <NUM>. This provides a desired flow of fuel through metering valve.

<FIG> illustrates another example of a fluid flow system <NUM>. To the extent not otherwise described or shown, the fluid flow system <NUM> corresponds to the fluid flow system <NUM> of <FIG> and <FIG>, with like parts having reference numerals preappended with a "<NUM>. " The EMID <NUM> in the system <NUM> is a single stage servo valve (SSSV) <NUM>. The SSSV <NUM> is in communication with a high pressure source <NUM> and a low pressure source <NUM>. The SSSV <NUM> includes a flapper <NUM> that moves in response to current through a torque motor <NUM>. Fluid flowing through the flapper <NUM> flows from the fluid sources <NUM>, <NUM> to the first fluid line <NUM> and then to the metering valve <NUM>. Electronic control <NUM> controls the torque motor <NUM> to achieve a desired mix between lines <NUM> and <NUM> into line <NUM>.

The fluid line <NUM> connects the SSSV <NUM> to a first chamber <NUM> of the metering valve <NUM>. A second chamber <NUM> is in communication with the second fluid source <NUM>. A third chamber <NUM> is in communication with source <NUM>. A fluid pressure difference between the first and third chambers <NUM>, <NUM> in combination, acts against a mixed flow from line <NUM> in chamber <NUM>. This moves the spool <NUM> to modulate fluid flowing to the nozzle <NUM> through line <NUM>. As spool <NUM> moves an annulus <NUM> selectively controls flow between inlet line <NUM>, from source <NUM>, and to outlet line <NUM>. Control <NUM> controls the mixed pressure on line <NUM> to position spool <NUM>.

An orifice <NUM> arranged along the first fluid line <NUM> between the SSSV <NUM> and the metering valve <NUM> limits the pressure of fluid flowing into the first chamber <NUM>. The fixed orifice <NUM> limits the slew rate of the metering valve <NUM> by preventing large pressure differences between the chambers <NUM>/<NUM> and <NUM>.

In the event of a failure of the EMID <NUM>, <NUM>, it is possible high pressure fluid only may be directed to one side of either metering valve <NUM>, <NUM>, causing a high slew rate. A high slew rate of the metering valve <NUM>, <NUM> would be undesirable. The fixed orifices <NUM>, <NUM>, <NUM> arranged between the EMID <NUM>, <NUM> and the metering valve <NUM>, <NUM> help to ensure the metering valve <NUM>, <NUM> is not exposed to fluid pressure differentials above a predetermined threshold.

<FIG> shows an example orifice <NUM>. Although the example orifice <NUM> is shown, this description may also apply to the orifice <NUM> in <FIG> and orifice <NUM> in <FIG>. In this example, the orifice <NUM> is arranged along a pipe <NUM> and maintains valve slew rates at the metering valve <NUM> below a predetermined threshold. The orifice <NUM> has an inner diameter <NUM> that is smaller than a nominal diameter <NUM> of the pipe <NUM>.

As shown in <FIG>, the orifice <NUM> extends inward of the pipe <NUM> and is symmetric about the longitudinal axis <NUM> of the pipe <NUM>. In other words, the orifice <NUM> extends into the pipe <NUM> about a circumference of the pipe <NUM>. This configuration limits the slew rates during a failed EMID <NUM> condition by limiting the pressure of fluid flowing to the metering valve. Although a particular orifice <NUM> is shown, other orifice configurations may be used. The diameters <NUM>, <NUM> may be selected based on a particular application to maintain the slew rate below a predetermined threshold.

<FIG> shows another example orifice <NUM>. The orifice <NUM> is arranged within a housing <NUM>. In this example, a first screen <NUM> and a second screen <NUM> are arranged on opposite sides of restriction <NUM>. The screens <NUM>, <NUM> protect the restriction <NUM> from debris in the fluid.

<FIG> shows another example orifice <NUM>. The orifice <NUM> includes a housing <NUM>. A first screen <NUM> and a second screen <NUM> are arranged on opposite sides of the restriction <NUM>.

The disclosed system eliminates concerns about undesirably high slew rates with a simple construction using fixed orifices to maintain the valve slew rates within a safe range. This arrangement limits the slew rates when the EMID fails. This arrangement may reduce cost and weight and improve reliability of the fuel metering system.

While this disclosure specifically describes a metering valve in a fuel supply, it could be used in other applications. As examples, it could be used with actuators for other functions on an engine, such as for variable vane stator actuators, pneumatic valves, bleed valves, or other applications.

A fluid flow system under this disclosure could be said to include a metering valve having a spool, a first chamber, and a second chamber. A pressure difference between the first chamber and the second chamber is configured to move the spool to meter a fluid. The metering valve is in fluid communication with a use. An electromechanical meter interface device (EMID) is in fluid communication with at least one of the first and second chambers of the metering valve. The EMID is configured to meter fluid from a first source and a second source to at least one of the first chamber and the second chamber. The first source has a different pressure from the second source. At least one fixed orifice is arranged between the metering valve and the EMID.

The first chamber may be in communication with the EMID via a first fluid line and the second chamber is in communication with the EMID via a second fluid line. The at least one fixed orifice includes a pair of fixed orifices, with one of the fixed orifices on the first fluid line and one on the second fluid line.

Alternatively, one of the first and second chambers may be is in fluid communication with the EMID via a first line, and the other of the first and second chambers is in fluid communication with one of the first and second sources without passing through the EMID, and the fixed orifice is on the first line.

A fluid flow system under this disclosure could also be said to include a metering means for metering fluid flow from a fluid source to a use. Control valve means direct a fluid source mixed from a first fluid source and a second fluid source through a first line to control a volume of fluid metered by the metering means. Fixed restriction means on the first line limit a pressure from the control valve means reaching the metering means.

The metering means may be a spool valve. The control valve means may be an electromechanical interface device and the fluid restrictions means may be a fixed orifice.

Claim 1:
A fluid flow system comprising:
a main valve having a spool (<NUM>), a first chamber (<NUM>, <NUM>), and a second chamber (<NUM>, <NUM>), wherein a pressure difference between the first chamber (<NUM>, <NUM>) and the second chamber (<NUM>, <NUM>) is configured to move the spool (<NUM>) to control a fluid flow;
an electromechanical interface device "EMID" in fluid communication with at least one of the first and second chambers (<NUM>, <NUM>) of the main valve, the EMID configured to meter fluid from a first source and a second source to at least one of the first chamber (<NUM>, <NUM>) and the second chamber (<NUM>, <NUM>), wherein the first source has a different pressure from the second source; and characterized by
at least one fixed orifice arranged between the main valve and the EMID, and wherein the first chamber (<NUM>, <NUM>) is in communication with the EMID via a first fluid line (<NUM>) and the second chamber (<NUM>, <NUM>) is in communication with the EMID via a second fluid line (<NUM>), the at least one fixed orifice includes a pair of fixed orifices (<NUM>,<NUM>), with one of the fixed orifices on the first fluid line and one on the second fluid line, or wherein one of the first and second chambers (<NUM>, <NUM>) is in fluid communication with the EMID via a first line, and the other of the first and second chambers is in fluid communication with one of the first and second sources without passing through the EMID, and the fixed orifice is on the first line.