3308461 - 1036C overhead camshafts (2)
CAMSHAFTS
The camshaft on the inlet side rotates on
six bearings, the one on the exhaust side on five.
The camshafts are driven by a toothed belt
(
See subassembly 1032 TIMING SYSTEM
).
HYDRAULIC TAPPETS
The hydraulic tappets automatically
cancel the valve clearance during engine operation, with the advantage
of reducing:
- maintenance interventions
- engine noise.
Operation in open stage
When the camshaft cam acts on the cup (1)
and consequently the piston (2), the oil trapped in the chamber
(6), because the ball valve (4) closes, transmits the movement of
the piston (2) directly to the sleeve (3) and so to the valve. During
this stage, because of the high pressure to which it is subjected,
some of the oil in the chamber (6) leaks through the tiny gap between the
piston (2) and sleeve (3).Operation in closed stage
While the valve is closed, so that the tappet,
pushed by the action of the spring (5), follows the profile of the
cam, a vacuum is created inside the chamber (6) which causes the
ball valve (4) to open, allowing oil to enter. The oil entering
the chamber (6) replaces the oil which leaked out previously while
the valve was open.PHASE TRANSFORMER
Controlled directly by the fuel injection
control unit, the purpose of the timing variator is to vary the
timing of the inlet valves in accordance with the engine load and
required rpm.Operation in closed stage
When the closed stage is required (idle
speed and maximum power zone), the solenoid (1) is de-energized,
so the slide valve (2), pushed by the return spring (3), remains
raised, preventing the oil coming from the duct (A) from reaching
the variator.In this case the timing of the inlet valves
remains unchanged (closed).Operation in open stage (os)
When the open stage is required (medium
rpm with high torque), the solenoid (1) is energized, thus pushing
the slide valve (2) downwards.In this position, the oil coming from the
duct (A) enters the chamber (B) of the piston, and from here, through
a special hole, goes into the duct (C) in the piston.The oil can only emerge from this duct through
the top hole (in communication with the delivery pipe (D) to the
variator), since the bottom hole, as the slide valve (2) has lowered,
is not in communication with the discharge pipe (E).The oil passes through the duct (D) and
(F) and reaches the chamber (G), pushing in an axial direction towards
the engine the piston (4), which comprises outer helical teeth,
forcing it to rotate clockwise.Its rotation is transmitted via a straight-teeth
splined profile to the pinion (5) which, screwed onto the threaded
end of the camshaft (6), transmits rotation to the camshaft, thus
varying by 25° engine the timing of the inlet valves.When the solenoid is de-energized, the slide
valve (2) returns to its initial position, cutting off the flow
of pressurized oil to the piston (4), but allowing oil to return
to the discharge, thanks to the force of the return spring (7).The duct (D) lubricates the camshaft journal
in the various operating conditions.The oil which leaks into the chamber (H)
of the solenoid is discharged through the drain duct (E).