Internal-combustion engine with variable-operation valves and auxiliary hydraulic tappet

Claim 1

An internal-combustion engine comprising: at least one induction valve and at least one exhaust valve for each cylinder, each valve being provided with respective elastic means that brings back the valve into the closed position to control communication between a respective induction and exhaust ducts and a combustion chamber; a camshaft for operating the induction and exhaust valves of the cylinders of the engine by means of respective tappets, in which at least one of said tappets controls the respective induction or exhaust valve against the action of said elastic return means via the interposition of hydraulic means including a hydraulic chamber (C) containing fluid under pressure; said hydraulic chamber containing fluid under pressure being connectable, via a solenoid valve, to an outlet channel for decoupling the valve from the respective tappet and causing fast closing of the valve under the action of respective elastic return means; said hydraulic means further comprising an actuating piston associated to the stem of the valve and slidably mounted in a guide bushing, said piston being set facing a variable-volume chamber defined by the piston and the guide bushing, said variable-volume chamber being in communication with the hydraulic chamber (C) containing fluid under pressure by means of a communication port constituted by an end aperture of said guide bushing, said piston having an end appendage designed to be inserted into said end aperture during a final stretch of a closing stroke of the valve in order to restrict the communication port between said variable-volume chamber and said hydraulic chamber containing fluid under pressure, so as to slow down the stroke of the valve in proximity of its closing, wherein set between the valve stem and the aforesaid piston ( 21 ) for actuating the valve is an auxiliary hydraulic tappet, and wherein the aforesaid hydraulic tappet comprises an auxiliary piston slidably mounted inside the body of the actuating piston and having one end that is set inside the actuating piston and set facing a chamber within the actuating piston which is in communication with the hydraulic chamber containing fluid under pressure, and one end set outside the actuating piston, which is in contact with the end of the valve stem, elastic means being provided for bringing back said auxiliary piston into an end-of-stroke position in the direction of the valve stem.