Device for automatically varying the timing of a camshaft

A device for automatically varying the timing of a camshaft relative to the drive shaft of an internal combustion engine, the camshaft being supported by bearings lubricated by pressurized oil of the engine lubrication circuit, the camshaft being driven in timed relation with the drive shaft by a toothed pulley rigidly affixed with a tubular member, the device comprising a sleeve movable axially within the tubular member in order to connect the toothed pulley to the camshaft, the sleeve being constrained to the tubular member by means of a straight toothed splined connection and being constrained to the camshaft by means of a helical toothed connection, an annular piston being rigidly affixed with the sleeve, a circular plate being rigidly affixed with the camshaft, the circular plate with the tubular member and the annular piston forming a chamber, the chamber being integrally connected to the engine lubrication circuit which feeds the pressurized oil to the camshaft support bearings by passage means for permitting oil to flow to the chamber, a presized orifice in said passage means for controlling the rate of oil flow to said chamber, vent means coupled to said passage means downstream of said presized orifice for communicating the passage means to atmosphere, said vent means including axially movable valve means for opening and closing said vent means and thereby regulating the feed and discharge flow of oil through the passage means, said vent means being normally open to allow the discharge of oil from said chamber, the axially movable valve means being operationally connected to an electromagnetic linear actuator which receives a command in the form of an electric signal from an electronic central unit in response to signal received from prechosen engine parameter sensors whereby the axially movable valve means moves to close the vent means causing oil to flow to the chamber.