System and method for variable actuation of valves of an internal combustion engine

Method for controlling the operation of an internal combustion engine, wherein said engine comprises, for each cylinder:

• a combustion chamber,
• a first intake conduit and a second intake conduit and at least one exhaust conduit opening on said combustion chamber,
• a first intake valve and a second intake valve, respectively associated to said first intake conduit and said second intake conduit and at least one exhaust valve associated to said at least one exhaust conduit, said intake valves and said exhaust valves being provided with respective return springs which bias the valve towards a closed position,
• a camshaft for actuating the intake valves by means of respective tappets,
• wherein each intake valve is driven by a respective tappet against the action of said return spring with the interposition of hydraulic means including a volume of fluid under pressure towards which a pumping piston is facing which is associated to the valve tappet, said volume of fluid under pressure being adapted to communicate with the chamber of a hydraulic actuator associated with said intake valve,
• each intake valve being associated to at least one electrically-actuated control valve adapted to communicate said volume of fluid under pressure with a discharge channel, for the purpose of uncoupling said intake valve from the respective tappet and causing a quick closing of said intake valve due to the action of the respective return spring,
• at least one electronic controller is provided for controlling said at least one control valve for varying the opening and/or closing time and the lift of each intake valve as a function of one or more operative parameters of the engine,
• the two intake valves of each cylinder are controlled by a single cam of said camshaft through a single hydraulic circuit and the communication of the hydraulic actuators of the two intake valves with said discharge channel is controlled by two electrically-actuated control valves, both of an on/off two-position type, arranged in series with each other along a hydraulic line for communication between the pressure volume and the discharge channel, wherein said communication hydraulic line includes, starting from said pressure volume towards said discharge channel:
• a first branch-off point connected to the hydraulic actuator of a first intake valve,
• a second branch-off point connected to the hydraulic actuator of a second intake valve,
• wherein a first control valve of said control valves is arranged between said second branch-off point and the discharge channel,
• so that when said first control valve is closed, the communication with the discharge channel is interrupted for both the hydraulic actuators,
• the second control valve is arranged in said communication line between said two branch-off points,
• so that when said second control valve is closed:
• the actuator of the first intake valve is always in communication with the pressure volume, whereas a communication with the discharge channel is interrupted, independently from the condition of operation of the first control valve,
• the actuator of the second intake valve is no longer in communication with the pressure volume, independently from the condition of operation of the first intake valve,
• said electronic controller controls said control valves so as to partially or totally open only the first intake valve of each cylinder in a reduced condition of operation of the engine, below a predetermined load of the engine and/or below a predetermined speed of revolution of the engine, and so as to partially or totally open both the intake valves in the remaining operating conditions of the engine.