Internal-combustion engine with an electronically controlled hydraulic system for actuation of the valves and means for compensating changes in the operating conditions of the hydraulic fluid

A method for controlling the inlet and/or exhaust valves of an internal-combustion engine, said engine comprising:

• at least one inlet valve and at least one exhaust valve for each cylinder of the engine, each provided with respective elastic return means, which push the valve towards a closed position, for controlling respective inlet and exhaust ducts;
• at least one camshaft for actuating each inlet and exhaust valve of the cylinders of the engine by means of respective tappets, each inlet and exhaust valve being controlled by a respective cam of said camshaft,
• in which each of said tappets controls the respective inlet valve or exhaust valve against the action of said elastic return means by means of the interposition of hydraulic means, which include a pressurized fluid chamber,
• the pressurized fluid chamber associated to each inlet or exhaust valve being designed for being connected, by means of a solenoid valve, to an exhaust duct for the purpose of uncoupling the valve from the respective tappet and causing rapid closing of the valve as a result of the respective elastic return means;
• and
• in which each solenoid valve is controlled for varying the time and the stroke of opening of the respective inlet or exhaust valve according to one or more operating parameters of the engine,
• wherein the value of temperature of the hydraulic fluid is detected in the proximity of the aforesaid hydraulic means for actuation of the inlet and/or exhaust valves of the engine, and the value of viscosity of the hydraulic fluid is estimated according to the detected temperature value, and in that the aforesaid solenoid valve is controlled according to the estimated viscosity value.