Method and system for starting up an aircraft turbomachine by real-time regulation of air flow

1. A method for starting up an aircraft turbomachine with aid of a start-up system comprising at least:

one ventilation source able to produce and to provide a flow of air with a compressor fed by an air intake circuit regulated by at least one inlet valve located upstream of the compressor, said inlet valve being able to be controlled; and

at least one start-up turbine fed by said ventilation source via a pneumatic connection, connecting the compressor to said start-up turbine, a controllable start-up valve being arranged on the pneumatic connection upstream of the start-up turbine, said start-up turbine being able to produce, when subjected to the flow of air, a mechanical force making it possible to turn a rotor of the turbomachine for a purpose of the starting up,

wherein said method comprises following two successive steps, implemented automatically and repeatedly, so as to regulate an opening of said inlet valve in real time:

a first step of determining a valve control order for controlling the inlet valve, comprising:

a first sub-step of measuring a speed of rotation of the rotor of the turbomachine;

a second sub-step of comparing the measured speed of rotation of the rotor measured in the first sub-step with a predetermined speed value; and

a third sub-step of calculating a valve control order on the basis of result of the comparison; and

a second step of controlling the opening of said inlet valve in accordance with said valve control order.

2. The method as claimed in claim 1 , wherein said predetermined speed value varies as a function of time.

3. The method as claimed in claim 1 , wherein said turbomachine is a turbofan, and in that said speed of rotation is the speed of rotation of a high-pressure rotor of said turbofan.

4. The method as claimed in claim 1 , wherein control of the inlet valve provides a variation of the flow of air therethrough to obtain a progressive modification of the current speed of rotation of the rotor.

5. The method as claimed in claim 1 , wherein said predetermined speed value is a constant.

6. A system for starting up an aircraft turbomachine, said system comprising:

a ventilation source able to produce and to provide a flow of air with a compressor fed by an air intake circuit regulated by at least one inlet valve located upstream of the compressor, said inlet valve being able to be controlled;

at least one start-up turbine fed by said ventilation source via a pneumatic connection, connecting the compressor to said start-up turbine, a controllable start-up valve being arranged on the pneumatic connection upstream of the start-up turbine, said start-up turbine being able to produce, when subjected to the flow of air, a mechanical force making it possible to turn a rotor of the turbomachine for a purpose of the starting up; and

a control system capable of controlling at least said inlet valve,

wherein said control system comprises a control loop for controlling an opening of said inlet valve, comprising at least one sensor configured to measure a current speed of rotation of the rotor, and

wherein said control system is configured to determine a valve control order for controlling the inlet valve based on the measured current speed of rotation of the rotor measured by the at least one sensor and a predetermined speed value and to control the opening of said inlet valve in accordance with said valve control order.

7. The system as claimed in claim 6 , wherein said control system comprises a first control unit and a second control unit connected together, wherein said first control unit is configured to receive data, carry out processing operations and transmit a piece of control information to said second control unit, and wherein said second control unit is configured to control the opening of said inlet valve based on the piece of control information received from said first control unit.

8. The system as claimed in claim 6 , wherein control of the inlet valve provides a variation of the flow of air therethrough to obtain a progressive modification of the current speed of rotation of the rotor.