Method for controlling an internal combustion engine

1. A method for controlling an internal combustion engine ( 1 ) including a turbocharger ( 12 ) provided with a turbine ( 13 ) and with a compressor ( 14 ) and further comprising an intake manifold ( 4 ) which receives fresh air through an intake pipe ( 6 ) adjusted by a throttle ( 8 ) valve and a number (W) of cylinders ( 3 ) connected to the intake manifold ( 4 ) and wherein the air mass trapped in each cylinder ( 3 ) for each engine cycle is adjusted by a respective throttle intake valve, wherein throttle intake valves are controlled independently for each cylinder ( 3 ); the control method comprising steps of:

determining the total target torque (C i_objt ) required to be delivered for the operation of the internal combustion engine ( 1 );

determining a target number (Waobj) of active cylinders ( 3 ) to be controlled for injection and combustion, wherein the target number (Ws) of active cylinders ( 3 ) is any number from 0 to the number (W) of cylinders ( 3 );

determining a number (Ws) of inactive cylinders ( 3 ) which are controlled to intake the most air as possible by controlling the respective throttle intake valve and are determined as a function of the target number (Waobj) of active cylinders ( 3 ) to be controlled for injection and combustion;

determining a target pressure (Pobj) of the intake manifold that is such as to guarantee the total target torque (Ci_objt) required to be delivered for the operation of the internal combustion engine ( 1 ); and

controlling the throttle ( 8 ) valve to adjust the target intake manifold pressure (Pobj) so as to guarantee the target torque (Ci_objt) required to be delivered for the operation of the internal combustion engine ( 1 ) by the target number (Waobj) of active cylinders ( 3 ) to be controlled for injection and combustion;

the step of determining the target number of cylinders ( 3 ) to be controlled for injection and combustion, wherein the target number (Waobj) of active cylinders ( 3 ) is any number comprised between 0 and the number (W) of cylinders ( 3 ), comprises sub-steps of:

determining a temporary number (Watemp) of active cylinders ( 3 ) to be controlled for injection and combustion as a function of the engine point;

determining, during a preliminary step of setting up and tuning, a possible minimum and maximum spark advance efficiency value for achieving combustion, wherein the spark advance efficiency (etasa) is the combustion efficiency relative to the actuated spark advance, as a function of the deviation with respect to the optimal advance which is stored in specific maps in an electronic control unit ( 21 );

determining a necessary spark advance efficiency which should be actuated by the temporary number (Watemp) of active cylinders ( 3 ) in order to guarantee the total target torque (Ci_objt) required to be delivered for the operation of the internal combustion engine ( 1 );

comparing the necessary spark advance efficiency with the possible minimum and maximum spark advance efficiency value for combustion; and

updating the target number (Waobj) of active cylinders ( 3 ) as follows:

(a) causing the target number (Waobj) of active cylinders ( 3 ) to be equal to the temporary number (Watemp) of active cylinders ( 3 ) only when the necessary spark advance efficiency is comprised within the range defined by the possible minimum and maximum spark advance efficiency value; or

(b) when the necessary spark advance efficiency is lower than the minimum advance efficiency value, decreasing the temporary number (Watemp) of active cylinders ( 3 ) of a number of cylinders equal to a deviation number (Δ); or

(c) when the necessary spark advance efficiency is higher than the maximum spark advance efficiency value, increasing the temporary number (Watemp) of active cylinders ( 3 ) of a number of cylinders equal to the deviation number (Δ);

in case (b) and (c) determining a necessary spark advance efficiency which should be actuated by the updated number (Watemp) of active cylinders ( 3 ) in order to guarantee the total target torque (Ci_objt) required to be delivered for the operation of the internal combustion engine ( 1 ) and updating the target number (Waobj) of active cylinders ( 3 ) until the necessary spark advance efficiency is comprised within the range defined by the possible minimum and maximum spark advance efficiency value.

2. A method according to claim 1 and comprising the further steps of:

determining a reference number (Warif) of active cylinders ( 3 ) to be controlled, in use, for the injection and the combustion as a function of the engine operation point; and

initializing the temporary number (Watemp) of active cylinders ( 3 ) to be controlled, in use, for injection and combustion as a function of the engine operation point at the reference number (Warif) of active cylinders ( 3 ).

3. A control method according to claim 1 , wherein the deviation number (Δ) of cylinders ( 3 ) to be either of added to and subtracted from the combustion is equal to 2.

4. A control method according to claim 1 , wherein the air mass trapped in each cylinder ( 3 ) for each engine cycle is adjusted by a VVT (Variable Valve Timing) device, which acts so as to vary the timing of at least one of the intake valves and exhaust valves.

5. A control method according to claim 1 and comprising the further steps of:

determining the position of the respective intake valves of the target number (Waobj) of active cylinders ( 3 ) to be controlled, in use, for injection and combustion, both during the intake stroke and during the exhaust stroke and as a function of the engine operation point; and

controlling the respective intake valves of the target number (Waobj) of active cylinders ( 3 ) to be controlled, in use, for injection and combustion, both during the intake stroke and during the exhaust stroke.

6. A method according to claim 1 and comprising the further step of injecting fuel into said number (Ws) of inactive cylinders ( 3 ).