초록 ▼

A fuel system includes first and second drive assemblies that are independently drivable relative to one another. The second drive assembly has a speed that is selectively controlled based upon a desired fuel flow. A non-positive displacement pump is driven by the first drive assembly. The non-posit

A fuel system includes first and second drive assemblies that are independently drivable relative to one another. The second drive assembly has a speed that is selectively controlled based upon a desired fuel flow. A non-positive displacement pump is driven by the first drive assembly. The non-positive displacement pump provides a desired fuel pressure for the fuel system. A positive displacement pump is driven by the second drive assembly. The positive displacement pump meters a desired volume in response to the speed of the second drive assembly in a first rotational direction. The fuel flows from the pumps and passes through a bypass valve that acts as a minimum pressure shut-off valve. During shut-down of the first drive assembly, the bypass valve is opened by a solenoid and the rotational direction of the second drive assembly is reversed to a second rotational direction to evacuate fuel from the system with the positive displacement pump and return the fuel to the fuel tank.

대표청구항 ▼

What is claimed is: 1. A fuel system comprising: first and second drive assemblies independently drivable relative to one another, the second drive assembly having a speed selectively controlled based upon a desired fuel flow; a first non-positive displacement pump; a second non-positive displaceme

What is claimed is: 1. A fuel system comprising: first and second drive assemblies independently drivable relative to one another, the second drive assembly having a speed selectively controlled based upon a desired fuel flow; a first non-positive displacement pump; a second non-positive displacement pump driven by the first drive assembly, the second non-positive displacement pump configured to receive fuel from the first non-positive displacement pump and provide a desired fuel pressure; and a positive displacement pump driven by the second drive assembly in first and second rotational directions, the positive displacement pump in fluid communication with the first non-positive displacement pump, the positive displacement pump metering a desired volume in response to the speed in a first direction and evacuating fuel in the second direction. 2. The fuel system according to claim 1, wherein the first and second non-positive displacement pumps are each a centrifugal pump. 3. The fuel system according to claim 2, wherein the first drive assembly includes a turbine engine, and the second drive assembly includes an electric motor. 4. The fuel system according to claim 3, comprising an alternator driven by the turbine engine at a second speed, the centrifugal pumps driven by the turbine engine at the second speed with the alternator. 5. The fuel system according to claim 3, comprising a controller, wherein the pumps provide fuel to the turbine engine, and the controller determines a fuel demand for the turbine engine and provides a speed command to the electric motor corresponding to the desired fuel flow for satisfying the fuel demand. 6. The fuel system according to claim 1, wherein the first non-positive displacement pump and the positive displacement pump are fluidly connected in series with one another along a first fluid path, and the first and second non-positive displacement pumps are fluidly connected in series with one another along a second fluid path, the first and second fluid paths intersecting at a bypass valve. 7. The fuel system according to claim 6, comprising: a fuel delivery device; the bypass valve is fluidly arranged between the second non-positive and positive displacement pumps and fuel delivery device for selectively controlling the flow of fuel through the bypass valve, the bypass valve having open and closed positions, the bypass valve moving from the closed position to the open position in response to a predetermined fuel pressure and returning to the closed position at a low fuel pressure less than the predetermined fuel pressure; and an actuator moving the bypass valve from the closed position to the open position with the positive displacement pump operating in a second direction to evacuate fuel from the fuel delivery device. 8. The fuel system according to claim 7, wherein the pumps and fuel device fluidly connected to one another via the bypass valve in the open position. 9. The fuel system according to claim 7, wherein the controller commands the electric motor to rotate in the second direction and the actuator to move the bypass valve from the closed position to the open position in response to an engine shut-down signal. 10. The fuel system according to claim 7, wherein the actuator is a solenoid. 11. A method of regulating the flow of fuel through a fuel system comprising the steps of: a) providing fuel to an engine through an open bypass valve; b) initiating an engine shut-down command; c) closing the bypass valve upon reaching a predetermined fuel pressure; d) actuating the bypass valve to an open position; e) reversing a rotational direction of a pump to evacuate fuel through the bypass valve, wherein steps d) and e) are performed in response to performing step b). 12. The method according to claim 11, wherein step a) includes driving the pump with an electric motor during an engine start-up. 13. The method according to claim 11, wherein step a) includes pumping fuel through the bypass valve with a first pump and delivering the fuel to a second pump, the second pump pumping fuel through the bypass valve to a third pump, the third pump pumping fuel through the bypass valve to a fuel delivery device. 14. The method according to claim 13, wherein the first and third pumps are centrifugal pumps, and the second pump is a positive displacement pump. 15. The method according to claim 13, wherein the fuel delivery device is a flow divider valve. 16. The method according to claim 11, wherein step a) is performed through a first fluid path, and step e) is performed through a second fluid path that is separate from the first fluid path. 17. The fuel system according to claim 6, a fuel tank fluidly connected to the first non-positive displacement pump via the first fluid path, and fluidly connected to the positive displacement pump via a return flow path, the second fluid path and return flow path intersecting at a shut-off valve, the shut-off valve in an open position with the positive displacement pump in the second direction and in a closed position with the positive displacement pump in the first direction.