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A system and method is provided for controlling a variable displacement piston pump that supplies fluid to one or more loads. If fluid is being supplied through a metering valve to a load, then the variable displacement piston pump is controlled to operate in accordance with a variable flow/variable

A system and method is provided for controlling a variable displacement piston pump that supplies fluid to one or more loads. If fluid is being supplied through a metering valve to a load, then the variable displacement piston pump is controlled to operate in accordance with a variable flow/variable discharge pressure scheme. However, if fluid is not being supplied through the metering valve to the load, then the variable displacement piston pump is controlled to operate in accordance with a variable flow/constant discharge pressure scheme.

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1. A fluid supply system, comprising: a variable displacement piston pump including an adjustable hanger that is movable to a plurality of control positions, the variable displacement piston pump configured to receive a drive torque and, upon receipt of the drive torque, to supply fluid at a pump di

1. A fluid supply system, comprising: a variable displacement piston pump including an adjustable hanger that is movable to a plurality of control positions, the variable displacement piston pump configured to receive a drive torque and, upon receipt of the drive torque, to supply fluid at a pump discharge pressure and flow rate dependent on the control position of the adjustable hanger;a hanger actuator including a pump control pressure inlet port coupled to receive pump control fluid at a fluid pressure, the hanger actuator responsive to the fluid pressure of the pump control fluid to move the adjustable hanger to a control position; anda pump compensator including a mode control pressure port and a pump control pressure outlet port, the pump compensator pump control pressure outlet port in fluid communication with the hanger actuator pump control pressure inlet port, the pump compensator responsive to fluid pressure at the mode control pressure port to operate in either (i) a normal mode, in which the pump compensator controls the fluid pressure of the pump control fluid such that the variable displacement piston pump is controlled in accordance with a variable flow/variable discharge pressure scheme, or (ii) a shutdown mode, in which the pump compensator controls the fluid pressure of the pump control fluid such that the variable displacement piston pump is controlled in accordance with a variable flow/constant discharge pressure scheme. 2. The system of claim 1, wherein: the pump compensator further includes a reference pressure port, a first control pressure port, and a second control pressure port;the pump compensator, in the normal mode, is further responsive to fluid pressure at the first control pressure port and the second control pressure port to control the fluid pressure of the pump control fluid such that a pressure differential between the first control pressure port and the second control pressure port is at least substantially constant; andthe pump compensator, in the shutdown mode, is further responsive to fluid pressure at the first control pressure port and the reference pressure port to control the fluid pressure of the pump control fluid such that a pressure differential between the first control pressure port and the reference control pressure port is at least substantially constant. 3. The system of claim 2, further comprising: a metering valve disposed downstream of the variable displacement piston pump and including a variable area flow orifice; anda metering valve actuator coupled to receive fluid flow commands and operable, in response thereto, to adjust the variable area flow orifice. 4. The system of claim 3, wherein: the pump compensator, in the normal mode, controls the fluid pressure of the pump control fluid to maintain a substantially constant differential pressure across the metering valve. 5. The system of claim 3, wherein: the metering valve further includes an inlet port and an outlet port, and the variable area flow orifice disposed between the inlet port and the outlet port;the pump compensator first control pressure port is in fluid communication with the metering valve inlet port; andthe pump compensator second control pressure port is in fluid communication with the metering valve outlet port. 6. The system of claim 2, wherein the pump compensator comprises: a mode control valve responsive to fluid pressure at the mode control pressure port to move between a normal mode position and a shutdown mode position; anda compensator valve in fluid communication with the mode control valve and operable to control the fluid pressure of the pump control fluid such that: (i) when the mode control valve is in the normal mode position, the variable displacement piston pump is controlled in accordance with the variable flow/variable discharge pressure scheme, and(ii) when the mode control valve is in the shutdown mode position, the variable displacement piston pump is controlled in accordance with the variable flow/constant discharge pressure scheme. 7. The system of claim 6, wherein the mode control valve comprises: a valve body including a first fluid outlet port and a second fluid outlet port, and having an inner surface that defines a shuttle valve chamber, the shuttle valve chamber in fluid communication with the mode control pressure port, the reference pressure port, the first control pressure port, the second control pressure port, the first fluid outlet port, and the second fluid outlet port; anda shuttle valve movably disposed within the shuttle valve chamber and responsive to the fluid pressure at the mode control pressure port to move between (i) the normal mode position, in which the first control pressure port and the second control pressure port are in fluid communication with the first fluid outlet port and the second fluid outlet port, respectively, and (ii) the shutdown mode position, in which the reference pressure port is in fluid communication with the first fluid outlet port and the second fluid outlet port. 8. The system of claim 7, wherein the compensator valve comprises: a valve body including a first section and a second section, the first section having a first cross sectional area, the second section having a second cross sectional area that is less than the first cross sectional area, the valve body first section in fluid communication with the mode control valve first and second fluid outlets, the valve body second section in fluid communication with the pump control pressure outlet port, the reference pressure port, and the first control pressure port; anda valve element movably disposed within the valve body, the valve element comprising: a first spool disposed within the valve body first section and having a first diameter, the first spool dividing the valve body first section into first and second chambers, the first and second chambers in fluid communication with the mode control valve first and second fluid outlets, respectively, anda second spool coupled to, and fluidly isolated from, the first spool, the second spool having a second diameter that is less than the first diameter, the second spool disposed within the valve body second section,wherein the valve element is responsive to fluid pressure at the first control pressure port, and fluid pressure in the first and second chambers, to operate in either the normal mode or the shutdown mode. 9. The system of claim 3, further comprising: a boost pump disposed upstream of, and operable to supply a flow of fluid to, the variable displacement piston pump. 10. The system of claim 9 wherein: the variable displacement piston pump further includes a pump inlet in fluid communication with the boost pump; andthe pump compensator reference pressure port is in fluid communication with the pump inlet of the variable displacement piston pump. 11. The system of claim 9, further comprising: a shut-off valve disposed downstream of the metering valve and movable between an open position and a closed position. 12. The system of claim 11, wherein: the shut-off valve further includes a position control pressure port that is in fluid communication with the pump compensator mode control pressure port;the shut-off valve is responsive to fluid pressure at the position control pressure port to move between the open and closed positions;the pump compensator is in the normal mode when the shut-off valve is in the open position; andthe pump compensator is in the shutdown mode when the shut-off valve is in the closed position. 13. A fluid supply system, comprising: a variable displacement piston pump including an adjustable hanger that is movable to a plurality of control positions, the variable displacement piston pump configured to receive a drive torque and, upon receipt of the drive torque, to supply fluid at a pump discharge pressure and flow rate dependent on the control position of the adjustable hanger;a hanger actuator including a pump control pressure inlet port coupled to receive pump control fluid at a fluid pressure, the hanger actuator responsive to the fluid pressure of the pump control fluid to move the adjustable hanger to a control position; anda pump compensator including a mode control pressure port and a pump control pressure outlet port, the pump compensator pump control pressure outlet port in fluid communication with the hanger actuator pump control pressure inlet port, the pump compensator responsive to fluid pressure at the mode control pressure port to operate in either a normal mode or a shutdown mode, the pump compensator comprising: a mode control valve responsive to fluid pressure at the mode control pressure port to move between a normal mode position and a shutdown mode position; anda compensator valve in fluid communication with the mode control valve and operable to control the fluid pressure of the pump control fluid such that: (i) when the mode control valve is in the normal mode position, the variable displacement piston pump is controlled in accordance with a variable flow/variable discharge pressure scheme, and(ii) when the mode control valve is in the shutdown mode position, the variable displacement piston pump is controlled in accordance with a variable flow/constant discharge pressure scheme. 14. The system of claim 13, further comprising: a metering valve disposed downstream of the variable displacement piston pump and including an inlet port, an outlet port, and a variable area flow orifice;a metering valve actuator coupled to receive fluid flow commands and operable, in response thereto, to adjust the variable area flow orifice,wherein the pump compensator, in the normal mode, controls the fluid pressure of the pump control fluid to maintain a substantially constant differential pressure across the metering valve. 15. The system of claim 14, wherein: the pump compensator further includes a reference pressure port, a first control pressure port, and a second control pressure port, the pump compensator first control pressure port in fluid communication with the metering valve inlet port, the pump compensator second control pressure port in fluid communication with the metering valve outlet port;the compensator valve, when the mode control valve is in the normal mode position, is further responsive to fluid pressure at the first control pressure port and the second control pressure port to control the fluid pressure of the pump control fluid to maintain the substantially constant differential pressure across the metering valve; andthe compensator valve, in the shutdown mode, is further responsive to fluid pressure at the first control pressure port and the reference pressure port to control the fluid pressure of the pump control fluid such that a pressure differential between the first control pressure port and the reference control pressure port is at least substantially constant. 16. The system of claim 14, further comprising: a boost pump disposed upstream of, and operable to supply a flow of fluid to, the variable displacement piston pump,wherein the variable displacement piston pump further includes a pump inlet in fluid communication with the boost pump, andthe pump compensator reference pressure port is in fluid communication with the pump inlet of the variable displacement piston pump. 17. The system of claim 14, further comprising: a shut-off valve disposed downstream of the metering valve and including a position control pressure port in fluid communication with the pump compensator mode control pressure port, the shut-off valve responsive to fluid pressure at the position control pressure port to move between an open position and a closed position,wherein: the mode control valve is in the normal mode position when the shut-off valve is in the open position, andthe mode control valve is in the shutdown mode position when the shut-off valve is in the closed position.