Method for controlling the speed of an internal combustion engine supercharged by means of a turbocharger

1. A method for controlling an internal-combustion engine ( 1 ) supercharged by a turbocharger ( 12 ) provided with a turbine ( 13 ) and compressor ( 14 ), said control method comprising steps of:

determining a current reduced-mass-flow rate (QAHR) of the compressor ( 14 );

determining a safety threshold (Mmax_turbo) of the reduced-mass-flow rate (QAHR) that delimits in a “reduced-mass-flow rate/compression ratio” plane an area substantially close to achievement of sonic conditions; and

imposing that the current reduced-mass-flow rate (QAHR) has to be lower than a safety threshold (Mmax_turbo) of the reduced-mass-flow rate (QAHR).

2. A control method as set forth in claim 1 , wherein said control method comprises further steps of:

establishing a predetermined limit speed (N) of the compressor ( 14 );

calculating a reduced limit speed (NR) of the compressor ( 14 ) by using the predetermined limit speed (N) and an absolute temperature (To) upstream of the compressor ( 14 ); and

determining the safety threshold (Mmax_turbo) of the reduced-mass-flow rate (QAHR) according to the reduced limit speed (NR).

3. A control method as set forth in claim 1 , wherein said control method comprises further steps of:

determining a safety threshold (Nmax_turbo) of speed of the internal-combustion engine ( 1 ) according to the safety threshold (Mmax_turbo) of the reduced-mass-flow rate (QAHR); and

imposing that the speed has to be lower than the safety threshold (Nmax_turbo) of the speed.