Process and device for supplying the turbojets of an aircraft during automatic flight

A system for supplying fuel to the turbojets (M1 to M4) of a multijet aircraft (A) flying in automatic pilot mode, the driving parameter of each of said turbojets being the ratio EPR of the gas pressures at the outlet and at the inlet of the corresponding turbojet and said aircraft comprising:

• means (13 to 15) for measuring the current value (EPRm.1 to EPRm.4) of said driving parameter EPR for each of said turbojets;
• means (16) for measuring the current value (N1m.1 to N1m.4) of the speed of rotation N1 of the fan of each of said turbojets,
• while said supply system consists of a plurality of supply devices (D1 to D4) each of which is associated with one of said turbojets and comprises:
• a first computer (20.1 to 20.4) producing, on the basis of the automatic thrust order and of the current flight conditions, a preset value EPRt for said driving parameter EPR, said preset value EPRt being identical for all the turbojets (M1 to M4);
• a slaving device (23.1 to 23.4) receiving said preset value EPRt and the corresponding current measured value (EPRm.1 to EPRm.4) of said driving parameter EPR and tending to align said current measured value with said preset value EPRt;
• a second computer (26.1 to 26.4) controlled by said slaving device (23.1 to 23.4) and computing the flow rate of fuel to be fed to said engine so as to align said current measured value of the driving parameter with the preset value;
• and
• fuel supply means (27.1 to 27.4) controlled by said second computer and delivering to said engine the flow rate of fuel computed by the latter,
• wherein:
• each supply device (D1 to D4) comprises, in parallel with said device (23.1 to 23.4) for slaving to said corresponding preset value EPRt, the arrangement in series:
• of a conversion table (T), identical for all said supply devices (D1 to D4) and connected to said first computer (20.1 to 20.4) so as to receive said preset value EPRt, said conversion table (T) being able to convert said preset value EPRt into a preset value N1t of said speed of rotation N1;
• and
• of a slaving device (24.1 to 24.4) receiving said preset value N1t and the corresponding current measured value (N1m.1 to N1m.4) of said speed of rotation N1 intended to align this current measured value with said preset value N1t;
• and
• each supply device (D1 to D4) comprises, between said devices (23.1 to 23.4–24.1 to 24.4) for slaving to the preset values EPRt and N1t, on the one hand, and said second computer (26.1 to 26.4), on the other hand, a switching means (25.1 to 25.4) able to connect to the latter, in a first state, said slaving device (23.1 to 23.4) associated with the preset value EPRt, and, in a second state, said slaving device (24.1 to 24.4) associated with the preset value N1t;
• and
• said switching means (25.1 to 25.4) are controlled in common by a control device (29) so as to toggle from said first state to said second state when the aircraft (A) is in automatic level flight at steady altitude.