Method of controlling knocking in an internal combustion engine equipped with a device for controlling the opening of inlet valves

1. A method of controlling knocking in an internal-combustion engine ( 1 ) equipped with a plurality of cylinders ( 2 ), a plurality of inlet valves ( 6 ) of the cylinders ( 2 ), and a device ( 11 ) to control opening of the inlet valves ( 6 ), wherein the method comprises steps of:

calculating, for each combustion of each of the cylinders ( 2 ), a knocking index (I KN ) representing a level of knocking of the combustion;

comparing the knocking index (I KN ) with a first threshold value (S 1 ) that indicates a maximum acceptable knocking;

determining presence of knocking in the cylinders ( 2 ) when the knocking index (I KN ) exceeds the first threshold value (S 1 );

comparing the knocking index (I KN ) with a second threshold value (S 2 ) that indicates presence of “megaknock” events;

determining the presence of the “megaknock” events in the cylinders ( 2 ) when the knocking index (I KN ) exceeds the second threshold value (S 2 );

reducing a mass of air sucked into the cylinder ( 2 ) in which the knocking occurs by acting on the device ( 11 ) for the control of the opening of valves that controls the inlet valves ( 6 ) while reducing an ignition advance in the cylinder ( 2 ) in which the knocking occurs; and

making, in the cylinder ( 2 ) in which the “megaknock” occurs, a decrease in an amount of the air sucked by acting on the device ( 11 ) for the control of the opening of the valves that controls the inlet valves ( 6 ) without carrying out any work on the ignition advance.

2. The control method as set forth in claim 1 , wherein the method comprises further a step of reducing the mass of the air sucked into the cylinder ( 2 ) starting from an engine cycle after an engine cycle in which there is the knocking.

3. The control method as set forth in claim 1 , wherein the method comprises further a step of not decreasing the mass of the air sucked in the cylinders ( 2 ) in which the knocking index (I KN ) does not exceed the first threshold value (S 1 ).

4. The control method as set forth in claim 1 , wherein the method comprises further steps of:

establishing a minimum ignition advance;

comparing, in case of the knocking in a cylinder ( 2 ), an actual ignition advance of the cylinder ( 2 ) to the minimum ignition advance; and

decreasing the actual ignition advance to limit the knocking in the cylinder ( 2 ) only if the actual ignition advance is greater than the minimum ignition advance.

5. The control method as set forth in claim 4 , wherein the method comprises further a step of not decreasing the actual ignition advance beyond the minimum ignition advance.

6. The control method as set forth in claim 5 , wherein the method comprises further a step of intervening by reducing the mass of the air sucked into the cylinder ( 2 ) in which there is the knocking when the ignition advance is equal to the minimum ignition advance.

7. The control method as set forth in claim 4 , wherein the method comprises further steps of:

starting with, in case of the knocking in a cylinder ( 2 ), a reduction of the actual ignition advance down to, if necessary, the minimum ignition advance; and

proceeding with a reduction in the amount of the air sucked into cylinder ( 2 ) in which the knocking occurred only when the actual ignition advance has reached the minimum ignition advance.

8. The control method as set forth in claim 4 , wherein the method comprises further a step of operating simultaneously in the cylinder ( 2 ) in which the knocking occurs a reduction in the actual ignition advance and amount of the air sucked.

9. The control method as set forth in claim 4 , wherein the method comprises further steps of:

determining for each cylinder ( 2 ) a standard ignition advance; and

gradually increasing the actual ignition advance starting from the standard ignition advance until a desired level of the knocking is reached to optimize the combustion.

10. The control method as set forth in claim 9 , wherein the minimum ignition advance is equal to the standard ignition advance.

11. The control method as set forth in claim 1 , wherein the method comprises further a step of engaging, together with a decrease of the mass of the air sucked into a cylinder ( 2 ), a similar decrease in a mass of fuel injected into the same cylinder ( 2 ) to not vary an air/fuel ratio.

12. The control method as set forth in claim 1 , wherein operation of the control device ( 11 ) allows variation for each cylinder ( 2 ) and, for each engine cycle, the actual opening of each inlet valve ( 6 ) independently of other inlet valves ( 6 ).

13. The control method as set forth in claim 1 , wherein the method comprises further a step of reducing, in case of “megaknock,” a boost pressure by acting on a turbocharger to further reduce density of charge in the cylinders ( 2 ).