The camshafts are made from spheroid cast iron, driven directly by the toothed belt.The inlet side camshaft rotates on eight supports and the exhaust side one rotates on seven supports.There are oil seals for the camshafts at the front.
PHASE TRANSFORMER
Specifications
System details
An electronically controlled phase transformer with hydraulic implementation for the inlet side camshaft has been adopted.Operated directly by the injection control unit, the phase transformer is designed to vary the timing of the inlet valves according to the engine speed and load conditions.The control unit recognizes malfunctions in the phase transformer or the electrical circuit and prevents operation.
Operation
Operation in closed stage (fc)
When the closed stage is requested (idle speed and maximum power zone), the electro-magnet (1) is de-energized, therefore the valve body (2), thrust by the opposing spring (3), remains raised, not allowing the oil arriving from the ducts (A) to reach the phase transformer.In this case, the valve timing remains unaltered (closed).
Operation in open stage (fa)
When the open stage is requested (average speeds at high torque). The electro-magnet (1) is energized, pushing the valve body (2) downwards.In this position, the oil, coming from the ducts (A), enters the piston chamber (B) and from there the channel (C) via a special port.From the above channel, the oil can only leave via the upper port (in contact with the oil supply duct (D) to the phase transformer). As the valve body (2) is lowered, the lower port is not in contact with the drainage duct (E).On reaching the chamber (G) via the ducts (D) and (F), the oil, moving the piston (4) axially, towards the engine which, having helical teeth on the outside, is forced to rotate in a clockwise direction.The rotation is transmitted, by means of a splined profile with straight teeth, to the pinion (5) which, bolted onto the threaded end of the camshaft (6), transmits the rotation to the shaft, altering the inlet valve timing by 18° .When the electro-magnet is de-energized, the valve body (2) returns to its original position, interrupting the flow of oil under pressure to the piston (4), but allowing the oil to return to the drain, thanks to the thrust of the opposing spring (7).The ducts (L) allow the lubrication of the camshaft bearing in all operating conditions.The oil which reaches the electro-magnet chamber (H) is drained through the drainage duct (E).
TAPPETS
Specifications
Type
The hydraulic tappets automatically cancel the valve clearance during the operation of the engine with the advantage of reducing:
maintenance operations
engine noise.
Operation
Operation in open stage
When the camshaft cam acts on the tappet (1) and consequently on the piston (2), as a result of the closure of the ball valve (4), the oil in the chamber (6) transmits the movement of the piston (2) directly to the hose (3) and, as a result, to the valve.During this stage, given the high pressure to which it is subjected, some of the oil in the chamber (6) flows through the minimal gap existing between the piston (2) and the hose (3).
Operation in closed stage
In order that the tappet, thrust by the action of the spring (5), follows the cam profile, a vacuum is created inside the chamber (6) that causes the opening of the ball valve (4), allowing the intake of oil.The oil introduced into the chamber (6) replaces that which escaped during the previous valve opening stage.
