Fuel control for gas turbine engine

Abstract

Fuel control apparatus including a fuel conduit connected to receive pressurized fuel from a fuel pump and provided with fuel servo actuated metering valve means therein for controlling the rate of fuel flow therethrough to an engine. The fuel servo actuated metering valve is actuated by a fuel servo piston pressurized by a servo valve controlled fuel pressure differential derived from a predetermined fuel pressure differential maintained by a pressurizing valve downstream from and in series flow relationship with the metering valve. The metered fuel flow for actuating the servo piston is extracted from the fuel conduit upstream from the pressurizing valve and returned to the fuel conduit downstream from the pressurizing valve.

I claim: 
     
       1. Fuel control apparatus for a combustion engine comprising: a fuel supply conduit for conducting a flow of pressurized fuel from a pressurized source to said engine;   first positionable valve means operatively connected to said supply conduit for establishing a controlled flow of fuel therethrough to said engine;   first fuel pressure differential responsive means operatively connected to said first valve means for actuating the same;   second valve means operatively connected to said supply conduit in series flow relationship with said first valve means and downstream therefrom for creating a predetermined back pressure against fuel flow through said first valve means .[.and.]. .Iadd.by .Iaddend.restricting fuel flow .Iadd.in the supply conduit .Iaddend.to establish a predetermined fuel pressure differential .[.in said supply conduit.]..Iadd., said second valve having a wall that moves in an opened direction in response to said predetermined fuel pressure differential to allow fuel to flow to said engine; .Iaddend.   resilient means operatively connected to said second valve means for urging the same toward a closed position in opposition to the fuel pressure upstream therefrom   .[.second fuel pressure differential responsive means vented to said supply conduit upstream and downstream from said second valve means and responsive to the fuel pressure differential therebetween for actuating said second valve means in an opening direction in opposition to said resilient means;.]. .Iadd.to establish a minimum fuel pressure differential; .Iaddend.   first passage means connected to said supply conduit in parallel flow relationship with said second valve means;   second passage means connecting said first fuel pressure differential responsive means to said supply conduit downstream from said second valve means;   a restriction in said first passage means;   a .Iadd.first .Iaddend.variable area valve in said first passage means for controlling the fuel pressure intermediate said restriction and said variable area valve; and   control means responsive to a plurality of variable conditions of engine operation operatively connected to said variable area valve for actuating the same;   said first fuel pressure differential responsive means being .[.verted.]. .Iadd.vented .Iaddend.to said first passage means intermediate said restriction and said variable area valve and responsive to the fuel pressure differential between said intermediate fuel pressure and said fuel pressure in said second passage means.   
     
     
       2. Fuel control apparatus as claimed in claim 1 and further including: a restriction in said second passage means; and   third passage means having a restriction therein connecting said first passage means upstream from said restriction therein to said second passage means intermediate said restriction therein and said first fuel pressure differential responsive means.   
     
     
       3. Fuel control apparatus as claimed in claim 2 wherein: said restriction in said second passage means and said restriction in said third passage means are fixed and have equal flow areas.   
     
     
       4. Fuel control apparatus as claimed in claim 1 wherein: said pressurized source is a positive displacement fuel pump;   said first valve means includes a .Iadd.second .Iaddend.variable area valve for controlling the effective flow area of said supply conduit and a fuel bypass valve operatively connected to said supply conduit for maintaining a constant predetermined fuel pressure differential across said variable area valve.   
     
     
       5. Fuel control apparatus as claimed in claim 1 wherein: said variable conditions of engine operation includes position of a power lever and engine speed.   
     
     
       6. Fuel control apparatus as claimed in claim 5 wherein: said variable conditions of operation further include an engine operating air pressure related to engine power output.   
     
     
       7. Fuel control apparatus as claimed in claim 6 wherein: said variable conditions of engine operation further include the temperature and pressure of air consumed by the engine.   
     
     
       8. Fuel control apparatus as claimed in claim 1 wherein: said control means includes an electrically actuated proportional solenoid connected to said variable area valve and responsive to an electrical input signal; and   electronic means responsive to said plurality of variable conditions of engine operation for .[.producting.]. .Iadd.producing .Iaddend.said electrical input signal as a function of said variable conditions of engine operation.   
     
     
       9. Fuel control apparatus as claimed in claim 1 and further including: position signal generating means operatively connected to said first positionable valve means; and   means operatively connecting said position signal generating means and said control means for transmitting said position signal to said control means.   
     
     
       10. Fuel control apparatus as claimed in claim 1 and further including: first and second stop means operatively connected to said first positionable valve means for limiting movement of said first valve means in a closing and opening direction, respectively.   
     
     
       11. Fuel control apparatus as claimed in claim 8 and further including: an emergency fuel supply conduit connected at one end to said supply conduit upstream from said first valve means and at the opposite end to said supply conduit downstream from said second valve means;   normally closed third valve means in said emergency fuel supply conduit blocking fuel flow therethrough;   fourth valve means in said emergency fuel supply conduit for controlling the effective flow area thereof;   electrically actuated means operatively connected to said third valve means for actuating the same to an open position in response to an electrical power failure; and   means responsive to a plurality of variable conditions of engine operation operatively connected to said fourth valve means for actuating the same.   
     
     
       12. Fuel control apparatus as claimed in claim 10 wherein: said last named means includes a three dimensional cam contoured as a function of said plurality of variable conditions associated therewith which includes position of a power lever and atmospheric air pressure.