Fuel pump systems

A fuel pump system can include a motor and a pump connected to the motor. The pump can be configured to receive an inlet flow from an inlet line, to pressurize the inlet flow, and to output a pressurized flow to an output line for an engine. The system can include a bypass line disposed between the outlet line and the inlet line, and a bypass valve disposed on the bypass line and configured to allow pressurized flow to flow to the inlet line in an open state, and to prevent pressurized flow from flowing to the inlet line in a closed state. The bypass valve can be configured to allow pressurized flow to flow to the inlet line to circulate flow and to maintain a constant pressure on the output line.

FIELD

This disclosure relates to fuel pump systems (e.g., for aircraft).

BACKGROUND

Main frame pumps can be used to move the fuel from aircraft tanks to the engines, to move fuel from tank to tank, and to jettison the fuel in case of need, for example. Typically, main frame mounted fuel pumps are electric motor driven at fixed speed. By their nature these pumps are of the inducer (e.g., screw) type. They are sized to deliver the required flow and pressure at the takeoff condition. At cruise and idle the required pressure from the engine is reduced. With the reduced flow at cruise and idle, the pressure required to push the fuel to the engine is always lower. However, inducer pumps produce more pressure rise and take more power to drive at lower flows. Since, the majority of time, aircraft engines operate at idle and cruise, the fuel pumps draw too much power. Also, the motor has to be size for the maximum power it must output.

Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for improved fuel pump systems. The present disclosure provides a solution for this need.

SUMMARY

A fuel pump system can include a motor and a pump connected to the motor. The pump can be configured to receive an inlet flow from an inlet line, to pressurize the inlet flow, and to output a pressurized flow to an output line for an engine. The system can include a bypass line disposed between the outlet line and the inlet line, and a bypass valve disposed on the bypass line and configured to allow pressurized flow to flow to the inlet line in an open state, and to prevent pressurized flow from flowing to the inlet line in a closed state. The bypass valve can be configured to allow pressurized flow to flow to the inlet line to circulate flow. The bypass valve can be configured to maintain a constant pressure on the output line.

The constant pressure can be above a maximum required pressure in a maximum flow condition. The motor can be a constant speed motor configured to turn the pump at a constant speed at a constant horsepower.

The system can include a control module configured to operate the motor at a constant speed to turn the pump at a constant speed to produce the constant pressure. The bypass valve can be a pressure regulating valve (PRV), for example. The PRV can be configured to open as a function of pressure differential between the output line and the input line.

In certain embodiments, the PRV can be mechanical and driven by the pressure differential between the output line and the input line. Any suitable valve or control scheme thereof is contemplated herein.

In certain embodiments, the pump can be an inducer pump comprising an axial impeller. Any other suitable pump type, e.g., that generates a higher pressure at lower engine speeds when operated at a constant speed, is contemplated herein.

In accordance with at least one aspect of this disclosure, an aircraft can include an engine, and a fuel pump system having an output line connected to the engine. The fuel pump system can include any suitable fuel pump system disclosed herein, e.g., described above.

In accordance with at least one aspect of this disclosure, a method can include driving an inducer pump to pump fuel on an output line connected to an aircraft engine, wherein driving is done at a constant speed, and bypassing flow from the output line to the input line to maintain a constant pressure on the output line. In certain embodiments, the constant pressure can be at or above a takeoff flow pressure required by the engine at a takeoff power setting.

In certain embodiments, bypassing flow can include using a mechanical pressure regulating valve which opens as a function of pressure on the output line relative to an input line. In certain embodiments, driving the inducer pump can include using a motor that is too small to supply sufficient pressure at idle or low speed engine conditions without bypassing flow from the output line to the input line. The method can include any other suitable method(s) and/or portion(s) thereof.

DETAILED DESCRIPTION

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, an illustrative view of an embodiment of a fuel pump system in accordance with the disclosure is shown inFIG.1and is designated generally by reference character100. Other embodiments and/or aspects of this disclosure are shown inFIGS.2A and2B. Certain embodiments described herein can be used to reduce weight of fuel pump systems (e.g., in aircraft) as well as reducing unnecessary maximum line pressure. Any other suitable uses are contemplated herein.

Referring toFIG.1, a fuel pump system100can include a motor101and a pump103connected to the motor101. The pump103can be configured to receive an inlet flow from an inlet line105(e.g., connected to a tank107), to pressurize the inlet flow, and to output a pressurized flow to an output line109for an engine99(e.g., a turbomachine).

The system100can include a bypass line111disposed between the outlet line109and the inlet line105. The system100can include a bypass valve113disposed on the bypass line111and configured to allow pressurized flow to flow to the inlet line105in an open state, and to prevent pressurized flow from flowing to the inlet line105in a closed state. The bypass valve113can be configured to allow pressurized flow to flow to the inlet line105to circulate flow. The bypass valve113can be configured to maintain a constant pressure on the output line109.

The constant pressure can be above a maximum required pressure in a maximum flow condition (e.g., a takeoff flow condition for an aircraft engine). The motor101can be a constant speed motor configured to turn the pump103at a constant speed and at a constant horsepower.

In certain embodiments, the system100can include a control module115configured to operate the motor103at a constant speed to turn the pump103at a constant speed to produce the constant pressure. The control module115can include any suitable hardware and/or software module(s) configured to perform the disclosed function.

The bypass valve113can be a pressure regulating valve (PRV), for example. The PRV can be configured to open as a function of pressure differential between the output line109and the input line105. In certain embodiments, the PRV can be mechanical and driven by the pressure differential between the output line and the input line. For example, when pressure is higher (e.g., above a threshold) on the output line109relative to the input line105, the bypass valve113can begin to open, and can continuously open with more relative pressure. The amount of flow area through the valve113can be defined by the pressure differential, causing the pressure on the outlet line109to track a constant pressure. Any suitable valve or control scheme thereof is contemplated herein.

In certain embodiments, the pump103can be an inducer pump comprising an axial impeller (e.g., a screw as appreciated by those having ordinary skill in the art in view of this disclosure). Any other suitable pump type, e.g., that generates a higher pressure at lower engine speeds when operated at a constant speed, is contemplated herein.

As shown inFIG.2A, a pump system without bypassing flow using a constant speed inducer pump generates the largest pressure (e.g., up to about 80 psi) at lower fuel flow conditions (e.g., idle and cruise) which required flow lines and connections to be robust enough to withstand such high pressures. As can be seen, the horsepower required at the lowest flow is about twice that at the takeoff flow condition (e.g., 6 horsepower in the shown embodiment), which requires a motor sized to produce up to at least the highest horsepower shown. However, referring toFIG.2B, using the same pump but with the bypass of system100, the pump pressure and the input horsepower can stay constant across all flow regimes. The motor can be sized to be about half of the size and weight of the motor needed to drive a system of without bypass (e.g., as shown inFIG.2A), and the flow lines and connections can be smaller and lighter as they need not withstand as much pressure (e.g., about a third of previous maximum pressure).

In accordance with at least one aspect of this disclosure, an aircraft (not shown) can include an engine99, and a fuel pump system, e.g., system100, having an output line connected to the engine99. The fuel pump system can be or include any suitable fuel pump system disclosed herein, e.g., system100described above.

In accordance with at least one aspect of this disclosure, a method can include driving an inducer pump to pump fuel on an output line connected to an aircraft engine, wherein driving is done at a constant speed, and bypassing flow from the output line to the input line to maintain a constant pressure on the output line. In certain embodiments, the constant pressure can be at or above a takeoff flow pressure required by the engine at a takeoff power setting.

In certain embodiments, bypassing flow can include using a mechanical pressure regulating valve which opens as a function of pressure on the output line relative to an input line. In certain embodiments, driving the inducer pump can include using a motor that is too small to supply sufficient pressure at idle or low speed engine conditions without bypassing flow from the output line to the input line. The method can include any other suitable method(s) and/or portion(s) thereof.

Embodiments can utilize a bypass valve to maintain pressure on the output line at or about a required takeoff pressure. The bypass valve can compare pressure from the output line to that of the input line. As pressure increases on the pump outlet side, the valve can open more to recycle more flow to the pump and the pressure on the output line can remain at a constant pressure to the engine.

Embodiments can provide and electric motor driven main frame pump with a bypass line. A bypass pressure regulating valve can be added to the pump line and set to maintain the pump discharge pressure to the desired pressure rise, e.g., for takeoff pressure. In embodiments, the pump power draw can always be that from the takeoff flow. Embodiments can reduce the power draw at cruise and idle condition to about half, and the motor sizing power can also be reduced by half.

Traditional main frame pumps are sized for the takeoff condition. Inducer pumps take more power and make more pressure rise at lower flows when not needed. Also, traditional motor is sized for the maximum pump power at idle flows. The main frame pumps can be required to operate with low inlet pressure and at times with two phase flow. That, combined with the desire to run at higher speeds for weight reduction, can lead to the main frame pumps being of the inducer type. Inducer pumps used as main frame pumps deliver more pressure and take more power at partial flows. That makes the motor size and power draw larger than needed at these conditions. Certain embodiments can add a bypass line around the pump along with back pressure regulating valve to always maintain the pump discharge pressure at that required at takeoff.

At partial flows, such as cruise and idle, the pump can produce more pressure rise based on its natural characteristic. In certain embodiments, a PRV can bypass the flow difference between takeoff and idle, or cruise and maintain the discharge pressure at a fixed value. The consequence of that at the pump level is that the pump can always operate at the takeoff condition, which, by design, can be the most efficient condition. A motor driven pump with no such valve will draw about twice as much power at idle and cruise when compared to the same pump operated with a PRV bypass valve. Compared to other solutions, embodiments can saves a good amount of power, size, and weight for low cost.