Method and device for determining the air bleed on an aircraft turbojet engine

1. A method for determining an air bleed on an aircraft turbojet engine, carried out by an air bleed system comprising, in the direction of the air bleed: at least a first valve arranged on an air bleed duct on a high pressure compressor of the turbojet engine, with which a first pressure sensor is associated; a saturation valve arranged at an inlet of a precooler; said precooler; and a second pressure sensor, arranged at an outlet of the precooler, said second pressure sensor measuring a pressure at the outlet of the precooler and monitoring operation of the saturation valve, the method comprising:

determining a pressure value relative to the pressure at the outlet of the precooler; and

calculating an air bleed level using the determined pressure value,

wherein, the determining the pressure value includes:

calculating a first pressure value at the outlet of the precooler using the pressure measured by said first pressure sensor;

receiving a pressure measured by said second pressure sensor, which represents a second pressure value at the outlet of the precooler; and

selecting one of said first and second pressure values at the outlet of the precooler that is used for calculating said air bleed level.

2. The method as claimed in claim 1 , wherein the calculating the first pressure value at the outlet of the precooler includes:

measuring a pressure PHPV at a level of said first valve using said first pressure sensor;

measuring a pressure difference DPBAS across said precooler; and

calculating said first pressure value PBAS 1 at the outlet of said precooler using the following formula:

PBAS 1= PHPV−PRSOV−DPBAS

in which PRSOV represents a predetermined value, corresponding to a pressure loss between said first valve and the inlet of the precooler.

3. The method as claimed in claim 2 , wherein said first pressure value PBAS 1 is limited to a predetermined value.

4. The method as claimed in claim 2 , wherein said pressure difference DPBAS is determined by measurements made by two separate sensors.

5. The method as claimed in claim 1 , wherein:

said first pressure value is selected if said first and second pressure values are available and a difference between the first and second pressure values is greater than a predetermined threshold;

said second pressure value is selected if said first and second pressure values are available and the difference between the first and second pressure values is less than or equal to the predetermined threshold;

said first pressure value is selected if said first pressure value is available and said second pressure value is not available;

said second pressure value is selected if said first pressure value is not available and said second pressure value is available; and

none of the first and second pressures is selected if said first and second pressure values are not available.

6. The method as claimed in claim 1 , wherein the air bleed level is calculated in a form of a mass flow WBAS, using the following formula:

WBAS α =(( PBAS+DPBAS/ 2)/ TPCE )·( DPBAS/k )

in which:

α and k are empirically determined parameters;

PBAS is the selected pressure value, relative to the pressure at the outlet of the precooler;

DPBAS is pressure difference across the precooler; and

TPCE is temperature in the precooler.

7. A device for determining an air bleed on an aircraft turbojet engine, carried out by an air bleed system comprising, in the direction of the air bleed: at least a first valve arranged on an air bleed duct on a high pressure compressor of the turbojet engine, with which a first pressure sensor is associated; saturation valve arranged at an inlet of a precooler; said precooler; and a second pressure sensor, arranged at an outlet of the precooler, said second pressure sensor measuring a pressure at the outlet of the precooler and monitoring the operation of the saturation valve, said device comprising:

first means configured for determining a pressure value relative to the pressure at the outlet of the precooler; and

second means configured for calculating an air bleed level using the determined pressure value,

wherein said first means comprise:

means configured for calculating a first pressure value at the outlet of the precooler, using the pressure measured by said first pressure sensor, said first pressure value being limited to a predetermined value;

means configured for receiving a pressure measured by said second pressure sensor, which represents a second pressure value at the outlet of the precooler; and

means configured for selecting one of said first and second pressure values, which is transmitted to said second means for calculating said air bleed level.

8. An air bleed system for an aircraft, said system comprising a device as claimed in claim 7 for determining an air bleed on a turbojet engine of said aircraft.

9. An aircraft comprising a device as claimed in claim 7 for determining an air bleed on a turbojet engine of said aircraft.