Multi-cylinder internal combustion engine, with cylinders equipped with intake valve variable actuation systems having hydraulic circuits which cross each other
An internal-combustion engine has a plurality of cylinders each with two intake valves driven by respective pumping pistons operatively associated to cams of a camshaft, by respective hydraulic circuits. The hydraulic has its pressure chamber communicating with hydraulic actuators of the two intake valves, so that the two intake valves of each cylinder are controlled, via two different hydraulic circuits, by cams associated to two different cylinders. Each cam is configured to give rise to a cycle of opening and closing of each of the intake valves in an angular range of rotation of the crankshaft less than 180° such that, in each operating cycle of a cylinder, only the first intake valve initially opens and closes while the second intake valve remains closed, and then the second intake valve opens and closes while the first intake valve remains closed.
1. An internal combustion engine, comprising:
a crankshaft;
a plurality of cylinders configured to execute respective operating cycles in a predetermined firing order, each cylinder including:
a piston operatively connected to the crankshaft so as to reciprocate within the cylinder,
a first intake valve controlling a flow of intake air from a first intake duct, the first intake valve including a first hydraulic actuator and a first return spring, and
a second intake valve controlling a flow of intake air from a second intake duct, the second intake valve including a second hydraulic actuator and a second return spring;
a camshaft driven via the crankshaft, the camshaft including a plurality of cams respectively associated with each cylinder;
a plurality of hydraulic circuits respectively associated with each cam, each hydraulic circuit including:
a tappet configured to engage the associated cam of the associated cylinder,
a pressure chamber,
a pumping piston driven by the associated cam via the tappet, the pumping piston configured to act on the pressure chamber so as to transfer pressurized fluid towards (i) the first hydraulic actuator of the first intake valve of the associated cylinder, and (ii) the second hydraulic actuator of the second intake valve of a preceding cylinder, the preceding cylinder being a cylinder of the plurality of cylinders which immediately precedes the associated cylinder in the predetermined firing order, such that the first and second intake valves of the associated cylinder are respectively controlled via two different cams of the plurality of cams,
a pressurized-fluid accumulator, and
an electrically actuated control valve configured to selectively communicate said pressure chamber with the pressurized-fluid accumulator via a low-pressure exhaust channel such that, when said electrically actuated control valve is open, the pressurized fluid is discharged from the pressure chamber into said low-pressure exhaust channel so as to deactivate the first intake valve of the associated cylinder and/or the second intake valve of the preceding cylinder; and
an electronic controller configured to control each electrically actuated control valve as a function of engine load and engine speed,
wherein each electrically actuated control valve is further configured to be switched to at least one of:
a full-lift mode in which both intake valves of the hydraulic circuit operate in accordance with a lift profile of the associated cam,
an early-closing mode in which both intake valves of the hydraulic circuit operate in accordance with a lift profile that is reduced with respect to the lift profile of the associated cam, and
a partial deactivation mode in which only one intake valve of the hydraulic circuit is deactivated, and
wherein, during an intake stage of each cylinder, an opening and closing timing of the second intake valve occurs subsequent to an opening and closing timing of the first intake valve.
2. The internal-combustion engine according to claim 1 , wherein each electrically actuated control valve is a two-way, two-position solenoid valve.
3. The internal-combustion engine according to claim 1 , wherein each electrically actuated control valve is a three-way, three-position solenoid valve.
4. The internal combustion engine according to claim 1 , wherein, in each cylinder, a diameter of the first hydraulic actuator is different from a diameter of the second hydraulic actuator such that the first intake valve and the second intake valve exhibit different lifts.
5. The internal combustion engine according to claim 1 , wherein, in each cylinder, the first and second return springs include different spring loads and/or spring constants such that the first intake valve and the second intake valve exhibit different lifts.