Method and device for controlling the speed of rotation of a turbosupercharger in an internal-combustion engine

A device (10) for controlling the speed in an internal-combustion engine of a motor vehicle comprising:

• a compressor (9);
• a turbine (8), designed to drive said compressor (9) in rotation under the action of the exhaust gases of the engine (2);
• and a wastegate valve (12), designed to regulate the flow rate of the exhaust gases provided at input to the turbine (8);
• said control device (10) comprising a control unit (14) designed to govern said wastegate valve (12) for controlling the speed of rotation of the turbine (8) as a function of an objective supercharging pressure (POB) which indicates the value of the supercharging pressure that, on the basis of an objective map of the engine and of a set of parameters of engine is required at output from said compressor (9);
• said control device (10) being characterized in that it comprises:
• first sensor means (20a) for measuring the air pressure (PAMB) at input to said compressor (9);
• and in that said control unit (14) comprises:
• a calculating unit (15), which receives at input a set of parameters comprising a pre-set limit speed (Ntc), said air pressure (PAMB) measured at input to the compressor (9), and the mass flow rate (QAH) of said compressor (9), and is designed to process said parameters for determining, through a predetermined map (15a) that characterizes operation of the compressor (9), a limit supercharging pressure (SP1) correlated to the air pressure obtainable at output from the compressor (9) in a condition in which the turbine (8) turns at a speed substantially equal to the preset maximum limit speed (Ntc);
• a comparison unit (16), designed to verify whether the required objective supercharging pressure (POB) satisfies a pre-set relation with said calculated limit supercharging pressure (SP1), said pre-set relation being satisfied when said required objective pressure (POB) is higher than said limit supercharging pressure (SP1);and
• a driving unit (17), which, in the case where said pre-set relation is satisfied, is designed to govern said wastegate valve (12) for controlling the speed of rotation of the turbine (8) as a function of the limit supercharging pressure (SP1) so as to limit the speed of rotation of said turbosupercharger (7) to a value substantially equal to said pre-set limit speed (Ntc), and in the case where said pre-set relation is not satisfied, said driving unit (17) being able to actuate said wastegate valve (12) for controlling the speed of rotation of the turbine (8) as a function of the objective supercharging pressure (POB) so as to achieve a supercharging corresponding to the objective pressure (POB) itself.