Internal-combustion engine having a system for variable actuation of the intake valves, provided with three-way solenoid valves

1. An internal-combustion engine, comprising, for each cylinder:

a combustion chamber;

at least two intake ducts and at least one exhaust duct, which give out into said combustion chamber;

at least two intake valves and at least one exhaust valve, which are associated to said intake and exhaust ducts and are provided with respective return springs that push them into a closed position;

a camshaft for actuating the intake valves, by means of respective tappets;

wherein each intake valve is controlled by the respective tappet against the action of the aforesaid return spring by interposition of hydraulic means including a pressurized-fluid chamber facing which is a pumping plunger connected to the tappets of the at least two intake valves, a pressurized-fluid chamber being designed to communicate with a chamber of a hydraulic actuator associated to each intake valve;

a single solenoid valve, associated to the intake valves of each cylinder and designed to set in communication said pressurized-fluid chamber with an exhaust channel in order to decouple the intake valves from their respective tappets and cause fast closing of the intake valves as a result of the respective return springs; and

electronic control means, for controlling said solenoid valve so as to vary the instant of opening and/or the instant of closing and the lift of each intake valve as a function of one or more operating parameters of the engine,

said engine being characterized in that the solenoid valve associated to each cylinder is a three-way, three-position solenoid valve, comprising:

an inlet permanently communicating with said pressurized-fluid chamber and with the hydraulic actuator of a first of the at least two intake valves; and

two outlets communicating, respectively, with the hydraulic actuator of the second of at least to intake valves and with said exhaust channel,

said solenoid valve having the following three operating positions:

a first position, in which the inlet communicates with both of the outlets so that the actuators of both of the intake valves are set in a discharging condition, and the intake valves are both kept closed by their return springs;

a second position, in which the inlet communicates only with the outlet connected to the actuator of the second intake valve and does not communicate, instead, with the outlet connected to the exhaust channel, so that the pressure chamber is isolated from the exhaust channel, the actuators of both of the intake valves communicate with the pressure chamber, and the intake valves are hence both active; and

a third position, in which the inlet does not communicate with any of the two outlets, so that the aforesaid pressure chamber is isolated from the exhaust channel, and the aforesaid first intake valve is active, whilst the second intake valve is isolated from the pressure chamber and is consequently inactive.

2. The engine according to claim 1 , wherein a body of the hydraulic actuator of the first intake valve has an exhaust port connected to the exhaust channel, which is overstepped by a plunger of the actuator after a pre-set stroke of said plunger in such a way as to set in a discharging condition a chamber of the actuator and prevent a further movement of said plunger beyond said stroke.

3. The engine according to claim 1 , wherein it comprises a line for direct communication between an exhaust environment and the pressure chamber, with a non-return valve interposed in said line to enable a flow of fluid only in a direction of the pressure chamber.

4. The engine according to claim 1 , wherein a line is provided for direct communication between a line for supply of the actuator of the second intake valve and an environment common to the pressure chamber and to a line for supply of the actuator of the first intake valve, with a non-return valve interposed in said communication line to enable a flow of fluid only in a direction of the pressure chamber.

5. The engine according to claim 1 , wherein said solenoid valve comprises a valve body with a first mouth, a second mouth, and a third mouth that can be used for constituting one said inlet and the others said outlets of said solenoid valve, the solenoid valve further comprising:

a first open/close element and a second open/close element, co-operating, respectively, with a first contrast seat and a second contrast seat;

wherein said first open/close element and said first contrast seat are provided for controlling the passage of fluid from said first mouth to said third mouth; and

wherein said second open/close element and said second contrast seat are provided for controlling the passage of fluid from said first mouth to said second mouth;

and in that said solenoid can be actuated for impressing on said second open/close element:

a first movement whereby said second open/close element is brought into contact with said second contrast seat disabling the passage of fluid from said first mouth to said second mouth providing a switching from said first operating position to said second operating position,

a second movement, subsequent to said first movement, whereby said second open/close element moves said first open/close element against said first contrast seat disabling the passage of fluid from said first mouth to said third mouth and providing a switching from said second operating position to said third operating position,

wherein during said second movement the second open/close element is in contact with said second contrast seat, and

wherein moreover said first open/close element and said second open/close element are coaxial to one another and hydraulically balanced.