Patent ID: 6918364
Filing Date: 2005-07-19
Classification: F01L

Abstract:
1. A multicylinder internal-combustion engine, comprising: at least one intake valve and at least one exhaust valve for each cylinder, each valve being provided with respective elastic return means, which push the valve towards a closed position for controlling respective intake pipes and exhaust pipe; and at least one camshaft, for actuating the intake valves and exhaust valves of the engine cylinders by means of respective tappets; in which each intake valve is controlled by the respective tappet against the action of the aforesaid elastic return means by interposition of hydraulic means that include a pressurized fluid chamber; said pressurized fluid chamber being designed to be connected by means of a solenoid valve to an exhaust channel in order to uncouple the valve from the respective tappet and bring about fast closing of the valve as a result of the respective elastic return means; electronic control means for controlling each solenoid valve so as to vary the time and the opening stroke of the respective intake valve according to one or more operating parameters of the engine; in which associated to each intake or exhaust valve is a control piston slidably mounted in a guide bushing; in which said control piston faces a chamber with variable volume communicating with the pressurized-fluid chamber both via first communication means controlled by a non-return valve, which enables only passage of fluid from the pressurized-fluid chamber to the variable-volume chamber, and via second communication means, which enable passage of fluid between the two chambers in both directions; wherein said second communication means include hydraulic-braking means designed to cause a restriction of said second communication means in the final phase of closing of the valve of the engine; wherein set between the control piston and the stem of the valve is a hydraulic tappet comprising: a first outer bushing slidably mounted within said guide bushing and having an end wall in contact with a cooperating end of the stem of the engine valve, a second inner bushing slidably mounted within said first outer bushing and having one end in contact with a cooperating end of said control piston, a first chamber defined between said second bushing and said control piston, which is in communication with a passage formed within the fixed body, for feeding fluid under pressure to said first chamber; a second chamber defined between said first bushing and said second bushing, and a non-return valve controlling a passage in a wall of said second bushing for enabling passage of fluid only from said first chamber of the tappet to said second chamber of the tappet.