VARIABLE DISPLACEMENT PUMP (VDP) SYSTEMS WITH DRY-OUT CENTRIFUGAL MAIN PUMP

A fuel system a main fuel pump sub-system (MFP) with an inlet for receiving a supply of fuel from an inlet line. The MFP has a main outlet line configured to supply fuel to a main fuel throttle valve assembly (MFTV), and a cross-over outlet line. A variable displacement pump sub-system (VDPP) has a first inlet connected in fluid communication with the cross-over outlet line, a second inlet connected to a branch of the main outlet line, a first outlet line configured to connect to supply fuel to the MFTV, and a second outlet line configured to connect to supply fuel to an actuation system.

BACKGROUND

The present disclosure relates to pump systems, and more particularly to fuel pump systems such as those used in gas turbine engines aboard aircraft.

2. Description of Related Art

There is a desire in modern aircraft design to reduce how much horsepower the fuel system extracts from the gearbox. In single engine aircraft it can be particularly difficult to design without using inefficient centrifugal main pumps because of their high reliability. These aircraft designs can struggle with satisfying fuel system thermal management requirements at low power conditions when centrifugal pumps are at their most inefficient.

The conventional techniques have been considered satisfactory for their intended purpose. However, there is an ever present need for improved systems and methods for improved fuel systems and methods. This disclosure provides a solution for this need.

SUMMARY

A fuel system a main fuel pump sub-system (MFP) with an inlet for receiving a supply of fuel from an inlet line. The MFP has a main outlet line configured to supply fuel to a main fuel throttle valve assembly (MFTV), and a cross-over outlet line. A variable displacement pump sub-system (VDPP) has a first inlet connected in fluid communication with the cross-over outlet line, a second inlet connected to a branch of the main outlet line, a first outlet line configured to connect to supply fuel to the MFTV, and a second outlet line configured to connect to supply fuel to an actuation system.

The actuation system can be connected in fluid communication with the second outlet line for hydraulic actuation. A boost pump can be configured to pressurize fuel from a source and connected in fluid communication with the inlet of the MFP.

The MFP can include a filter in a centrifugal pump feed line. The filter can be connected in fluid communication with the inlet of the MFP. The MFP can include an inlet shut off valve (ISOV) in the centrifugal pump feed line downstream of the filter, wherein the ISOV is configured to switch between a first state blocking supply of fuel through the centrifugal pump feed line and a second state supplying fuel through the centrifugal pump feed line to the centrifugal pump.

The MFP can include a centrifugal pump connected in fluid communication with the centrifugal pump feed line downstream of the ISOV to be supplied with fuel from the filter with the ISOV in the second state. The centrifugal pump can have a centrifugal pump outlet in fluid communication with the main outlet line. The MFP can include a stabilizing check valve (SCV) in the main outlet line configured to allow flow from the centrifugal pump through the main outlet line, stabilize pump operation during large flow demand transients and to prevent backflow from the main outlet line into the centrifugal pump. The MFP can include a centrifugal pump bypass line connecting in fluid communication from the filter to a point in the main outlet line downstream of the SCV. The centrifugal pump bypass line can include a check valve (CV) configured to prevent backflow from the main outlet line to the filter.

An ejector can have a drain inlet connected to in fluid communication with a branch of the main outlet line that is upstream of the SCV, an ejection inlet connected in fluid communication with a return line from the MFTV, and an outlet connected in fluid communication with a return line configured to be connected to an inlet of a boost pump. The ejector can be configured to drain the centrifugal pump using flow from the VDPP through the MFTV.

The VDPP can include a variable positive displacement pump, with a pump inlet connected in fluid communication with the cross-over outlet line, and an outlet connected in fluid communication with a main VDPP pump outlet line connected in fluid communication with the second outlet line. The VDPP can include a check valve (CV) in the main VDPP pump outlet line, configured to prevent backflow through the main VDPP outlet line into the variable positive displacement pump. The VDPP can include an actuator selector valve (ASV) in the main VDPP pump outlet line downstream of the CV. The ASV can be connected to a branch of the main outlet line of the MFP to select between supplying the second outlet line from the variable positive displacement pump or from the main outlet line or from. The VDPP can include a selector valve (SV) connected in fluid communication with a branch of the main VDPP pump outlet line that is downstream of the ASV, and in fluid communication with the first outlet line. The SV can be configured to prevent flow from the VDPP to the MFTV in normal operation so the VDPP supplies an actuation system, and to allow flow from the VDPP to the MFTV with the MFP shut off in a low power mode.

The MFTV can be connected in fluid communication to receive fuel supplied from the VDPP and to output fuel to a gas generator (GG) during engine start-up, and to receive fuel supplied from the MFP and to output fuel to the GG after start-up. The MFTV can include an MFTV check valve (CV) connected in fluid communication between the main outlet line and the first outlet line of the VDPP, configured to prevent flow from the main outlet line to the first outlet line of the VDPP, and to allow flow from the first outlet line of the VDPP to the main outlet line.

The MFTV can include a selector valve (SV) connected in fluid communication with the first outlet line of the VDPP, with a branch of the main outlet line upstream of the CV, and with an engine line. The SV can be configured to select between the main outlet line and the first outlet line of the VDPP to supply fuel from the MFTV to the engine line. The MFTV can include a regulator connected between the first outlet line of the VDPP an augmentor fuel control line such that the regulator is configured to receive flow from the first outlet line of the VDPP and to output an augmentor fuel control flow. The MFTV can include a thermal recirculation line outlet in fluid communication with the main outlet line configured for supplying a thermal recirculation system.

An augmentor fuel control (AFC) can be connected in fluid communication with a line from the MFTV, with a branch of the main outlet line, and with a branch of the second outlet line for providing fuel to an augmentor from the VDPP or MFP as needed.

A first return line can be connected in fluid communication with the inlet of the MFP, configured to return flow from the actuation system. A second return line can be connected in fluid communication with an ejector of the MFP, configured to return flow from the MFP to an inlet of a boost pump. A third return line can be connected in fluid communication with the first return line, configured to return flow from an augmentor fuel control (AFC) to the first return line. A fourth return line can be configured to return flow from the MFTV to the MFP.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, a partial view of an embodiment of a system in accordance with the disclosure is shown inFIG.1and is designated generally by reference character100. The systems and methods described herein can be used to dry centrifugal pumps when not in use, and to supply downstream systems instead with a positive displacement pump for low power operation including start up, taxiing, and ground readiness as in aircraft operation.

The fuel system100includes a main fuel pump sub-system (MFP)102with an inlet104for receiving a supply of fuel from an inlet line106. The MFP102has a main outlet line108configured to supply fuel to a main fuel throttle valve assembly (MFTV)110and a cross-over outlet line128. A variable displacement pump sub-system (VDPP)124has a first inlet126connected in fluid communication with the cross-over outlet line128, a second inlet112connected to a branch114of the main outlet line108, a first outlet line132configured to connect to supply fuel to the MFTV110, and a second outlet line130configured to connect to supply fuel to an actuation system136, and to supply an augmentor fuel control122via the branch138of the line130.

The actuation system136is connected in fluid communication with the second outlet line for hydraulic actuation, e.g. wherein the aircraft uses fuel as a working fluid for hydraulics. A boost pump140is configured to pressurize fuel from a source such as a fuel tank (note that PFO from A/C inFIG.1indicates Pressure, Fuel0, the lowest available pressure in the fuel system, the pressure provided by the aircraft tank pumps) and is connected in fluid communication with the inlet104of the MFP102via the line106.

The MFP102includes a filter142in a centrifugal pump feed line144, wherein the filter142is connected in fluid communication with the inlet104of the MFP102. The MFP102includes an inlet shut off valve (ISOV)146in the centrifugal pump feed line144downstream of the filter142. The ISOV146is configured, based on a control signal from a controller148, to switch between a first state blocking supply of fuel through the centrifugal pump feed line144to the centrifugal pump150, and a second state supplying fuel through the centrifugal pump feed line144to the centrifugal pump150.

The MFP102includes the centrifugal pump150connected in fluid communication with the centrifugal pump feed line144downstream of the ISOV146to be supplied with fuel from the filter with the ISOV146in the second state. The centrifugal pump150has centrifugal pump outlet152in fluid communication with the main outlet line108. The MFP102includes a stabilizing check valve (SCV)154in the main outlet line108configured to allow flow from the centrifugal pump150through the main outlet line108, and to prevent backflow from the main outlet line108into the centrifugal pump150. The SCV154is utilized to stabilize the centrifugal main pump operation. The main pump150responds quickly to changes in downstream demands, but with the significant volume in the downstream system it takes a while for the response to be seen by the downstream system. This can lead constructive feedback and unstable oscillatory behavior so the SCV154acts as a damper to the main pump150.

An ejector160is included in the MFP102, having a drain inlet162connected to in fluid communication with a branch162of the main outlet line that is upstream of the SCV154, an ejection inlet164connected in fluid communication with the return line168from the MFTV110, and an outlet connected in fluid communication with a return line170connected to an inlet172of the boost pump140. The ejector164is configured to drain the centrifugal pump150using flow from the VDPP124through the MFTV110. This is a dry out system to reduce/minimize horsepower extraction by the centrifugal pump150when the VDPP124is supplying the MFTV110and the centrifugal pump150is shut down. This can be used for gas turbine engine start up, ground idle, taxi, other low power conditions. The actuation pump174of the VDPP124delivers the burn flow to the gas generator (GG) during such low power conditions. The main pump150is responsible for both augmentation and some or all of the operational regime of the main gas generator GG.

The VDPP124includes a variable positive displacement pump174, e.g., a bent axis piston pump. The pump174has a pump inlet connected in fluid communication with the cross-over outlet line128, and an outlet connected in fluid communication with a main VDPP pump outlet line176connected in fluid communication with the second outlet line130. The VDPP124includes a check valve (CV)178in the main VDPP pump outlet line176, configured to prevent backflow through the main VDPP outlet line176into the variable positive displacement pump174in the event of VDPP pump failure, when the MFP102is supplying the actuation system136in backup mode. The VDPP includes an actuator selector valve (ASV) in the main VDPP pump outlet line downstream of the CV. The VDPP124includes an actuator selector valve (ASV)184in the main VDPP pump outlet line176downstream of the CV178. The ASV184is configured, based on a signal from the controller148or passively based on pressure differentials, to select between supplying the second outlet line130from the variable positive displacement pump174in normal operation or from the main outlet line108in a backup mode in case of failure of the variable positive displacement pump174. The VDPP124includes a selector valve (SV)180connected in fluid communication with a branch of the main VDPP pump outlet line176that is downstream of the ASV184, and in fluid communication with the first outlet line132. The SV180is configured to prevent flow from the VDPP124to the MFTV110in normal operation so the VDPP124supplies the actuation system136without supplying the MFTV110, and to allow flow from the VDPP124to the MFTV110with the MFP102shut off in any of the low power modes.

The MFTV110is connected in fluid communication to receive fuel supplied from the VDPP124and to output fuel to a gas generator (GG) during engine start-up, and other low power modes as described above, and to receive fuel supplied from the MFP102and output fuel to the GG after start-up or when not in the other low power modes. The MFTV110includes an MFTV check valve (CV)190connected in fluid communication between the main outlet line108and the first outlet line132of the VDPP124, configured to prevent flow from the main outlet line108to the first outlet line132of the VDPP124when the VDPP124is not supplying fuel to the MFTV110, and to allow flow from the first outlet line132of the VDPP124to the main outlet line108otherwise.

The MFTV110includes a selector valve (SV)192connected in fluid communication with the first outlet line132of the VDPP124, with a branch194of the main outlet line108upstream of the CV190, and with an engine line196. The SV192is configured to select between the main outlet line108and the first outlet line132of the VDPP124to supply fuel from the MFTV110to the engine line196such for supplying fuel injectors in a gas turbine engine combustor. The SV192can be controlled by the controller148to change the state of the SV148based on the mode of operation, or in certain embodiments, the SV148can be passively controlled by pressure differential between the main outlet line108and the first outlet line132of the VDPP124. In the start-up and low power modes, the SV192can be configured to select the line132to supply fuel to the engine line196. Otherwise in other modes, (e.g., the normal run mode, or a failure mode wherein the pump174fails), the SV192can be configured to select the main outlet line108to supply fuel to the engine line196.

The MFTV110includes a regulator198connected between the first outlet line132of the VDPP124and an augmentor fuel control line200such that the regulator198is configured, e.g. based on control signals from the controller148, to receive flow from the first outlet line132and to output an augmentor fuel control flow to the AFC200in the startup and low power modes. The MFTV110includes a thermal recirculation line outlet202in fluid communication with the main outlet line108downstream of the CV190configured for supplying a thermal recirculation system (TR).

An augmentor fuel control (AFC) connected in fluid communication with a line220from the MFTV110, with a branch116of the main outlet line108, and with a branch138of the second outlet line130for providing fuel to an augmentor from the VDPP124or MFP102as needed based on mode of operation. There is no dedicated augmentor fuel pump, the AFC122is supplied from the MFP pump150, or from the VDPP pump174if needed. There are two routes for fuel from the VDPP124to the AFC122, i.e. line132and branch138, and the AFC has valving to allow the VDPP124to perform priming/control functions while the main pump is powered off.

InFIG.1, the solid lines are feed lines, and the dotted lines are return lines. A first return line228is connected in fluid communication with the inlet104of the MFP102, configured to return flow from the actuation system136. A second return line230is connected in fluid communication with the first return line228and is connected to return flow from the AFC122to the first return line228.

Systems and methods as disclosed herein allow the main pump150to be a selectable pump with a dry-out system to minimize horsepower extraction when turned off. The main pump150can be turned off at low power conditions such as ground idle, taxi, start up, and the like, and the actuation pump174can be allowed to deliver the burn flow. The main pump150is sized for some or all of the operational regime of the gas generator GG and augmentor. The VDPP124can potentially run a gas turbine engine up to 50% speed or more for startup, ground idle, taxiing, and the like. The main pump150does not feed the pump174of the VDPP, and there is no need for supercharging the pump174.

Systems and methods as disclosed herein provide potential benefits including the following. They can reduce fuel pump horsepower extraction. They can also reduce main pump turn down ratio, which improves overall efficiency. The methods and systems of the present disclosure, as described above and shown in the drawings, provide for drying centrifugal pumps when not in use, and to supplying downstream systems instead with a positive displacement pump for low power operation including start up, taxiing, and ground readiness as in aircraft operation. While the apparatus and methods of the subject disclosure have been shown and described with reference to preferred embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the scope of the subject disclosure.