Secondary fuel flow demand fuel pumping system

Abstract

A fuel system for a gas turbine engine includes a main fuel pump generating a main fuel flow into a main fuel passage and a secondary pump generating a secondary fuel flow into a secondary flow passage. A first control valve is disposed in a passage between the main fuel passage and the secondary flow passage. The first control valve selectively directs an excess portion of the main fuel flow to the secondary flow passage to provide at least a portion of the secondary fuel flow.

What is claimed is: 
     
         1 . A fuel system for a gas turbine engine comprising:
 a main fuel pump generating a main fuel flow into a main fuel passage;   a secondary pump generating a secondary fuel flow into a secondary flow passage; and   a first control valve disposed in a passage between the main fuel passage and the secondary flow passage, wherein the first control valve selectively directs an excess portion of the main fuel flow to the secondary flow passage to provide at least a portion of the secondary fuel flow.   
     
     
         2 . The fuel system as recited in  claim 1 , including a boost pump drawing fuel from a fuel supply and directing fuel flow to the main fuel pump and the secondary pump. 
     
     
         3 . The fuel system as recited in  claim 2 , including an electric motor driving the secondary pump. 
     
     
         4 . The fuel system as recited in  claim 2 , including a second control valve disposed between the boost pump and the secondary pump, the second control valve selectively reducing fuel flow to the secondary pump in response to communication of excess fuel flow from the main passage to the secondary flow passage. 
     
     
         5 . The fuel system as recited in  claim 4 , including a common shaft driving each of the boost pump, main pump and secondary pump. 
     
     
         6 . The fuel system as recited in  claim 5 , including a selectively actuated clutch for decoupling the secondary pump from the common shaft. 
     
     
         7 . The fuel system as recited in  claim 5 , wherein the main pump is disposed between the boost pump and the secondary pump. 
     
     
         8 . The fuel system as recited in  claim 1 , wherein the secondary pump provides the secondary fuel flow to an ejector pump disposed within a fuel tank. 
     
     
         9 . The fuel system as recited in  claim 1 , wherein the secondary pump provides the secondary fuel flow to operate an actuator. 
     
     
         10 . The fuel system as recited in  claim 1 , wherein the main pump comprises a constant volume gear pump. 
     
     
         11 . A gas turbine engine comprising:
 a fan rotatable within a fan nacelle;   a core engine including a compressor communicating compressed air to a combustor where compressed air is mixed with fuel and ignited to generate a high-energy gas flow expanded through a turbine;   an accessory gearbox driven by a mechanical link to the turbine; and   a fuel system including;
 a fuel tank including an ejector pump; 
 a main fuel pump drawing fuel from the fuel tank and generating a main fuel flow into a main fuel passage; 
 a secondary pump generating a secondary fuel flow within a secondary flow passage in communication with the ejector pump; and 
 a first control valve disposed in a passage between the main fuel passage and the secondary flow passage, wherein the first control valve selectively directs an excess portion of the main fuel flow to the secondary flow passage to provide the secondary fuel flow. 
   
     
     
         12 . The gas turbine engine as recited in  claim 11 , including a boost pump drawing fuel from the fuel tank and directing fuel flow to the main fuel pump and the secondary pump. 
     
     
         13 . The gas turbine engine as recited in  claim 12 , including a second control valve disposed between the boost pump and the secondary pump, the second control valve selectively shutting off fuel flow to the secondary pump in response to communication of excess fuel flow from the main passage to the secondary flow passage. 
     
     
         14 . The gas turbine engine as recited in  claim 12 , including a common shaft driving each of the boost pump, main pump and secondary pump. 
     
     
         15 . The gas turbine engine as recited in  claim 14 , wherein the common shaft is driven by an output of the accessory gearbox. 
     
     
         16 . The gas turbine engine as recited in  claim 14 , including a selectively actuated clutch for decoupling the secondary pump from the common shaft. 
     
     
         17 . The gas turbine engine as recited in  claim 12 , including an electric motor for driving the secondary pump. 
     
     
         18 . A method of supplying fuel to a combustor of a gas turbine engine comprising:
 generating a main fuel flow with a main fuel pump and communicating the main fuel flow to a main fuel passage in communication with the combustor;   generating a secondary flow with a secondary pump and communicating the secondary flow to a secondary flow passage; and   bypassing an excess fuel flow from the main fuel passage into the secondary flow passage to generate at least a portion of the secondary flow.   
     
     
         19 . The method as recited in  claim 18 , including supplying fuel flow from a boost pump to the secondary pump and the main fuel pump during a first engine operating condition requiring a first fuel flow and stopping fuel flow to the secondary fuel pump during a second engine operating condition requiring a second fuel flow, wherein the second fuel flow includes the excess fuel flow. 
     
     
         20 . The method as recited in  claim 18 , including deactivating the secondary fuel pump such that the secondary fuel pump stops running in response to excess fuel flow from the main fuel passage generating a predefined fuel flow that is sufficient to meet secondary fuel flow demands.