Fiat 1996 Brava Service Manual page 338

Engine Bravo i0»
2
ov
Fuel system 98 range
10.
PHASE TRANSFORMER
In order to achieve a good compromise between good performance in terms of power at high speeds
and good torque at low speeds, a phase transformer (with electronic operation and hydraulic implemen­
tation) has been fitted on this engine for the inlet camshaft.
This device makes it possible to vary the timing diagram (inlet stroke) according to the load required by
the engine; this parameter is processed by the MOTRONIC control unit on the basis of the electrical sig­
nals received by the air flow meter and the rpm sensor and is sent as a commant to the phase transformer
solenoid valve.
The construction of the device involves a main assembly fitted on the inlet camshaft which is designed
to alter the angular position of the actual shaft in relation to the drive pulley.
In addition, there is an impelementation valve, operated by a solenoid valve, both on which are on the inlet
manifold and are hydraulically connected to the main assembly by means of suitable ducts.
The operating principle is as follows:
- with the temperature of the coolant below 40 °C and when the engine is idling or the speed exceeds a
pre-set level, the solenoid valve (1) is de-energized, therefore the valve body (2), thrust by the op­
posing spring (3), remains raised not allowing the oil, which is arriving from the duct (A), to reach the
transformer.
In this case the timing of the inlet valves remains unaltered.
With the coolant temperature above 40 °C and the engine speed below a pre-set level with the butter­
fly angle greater than around 8°, the solenoid valve (1) is energized, thereby pushing the valve body
(2) downwards. In this position, the oil, coming from the duct (A), enters the piston chamber (B) and
from there flows through a special port into the duct (C) inside the latter.
The oil can only leave the above mentioned duct through the upper port (in contact with the oil sup­
ply duct to the transformer (D)) because the lower port is not in contact with the drainage duct (E) as
the valve body (2) is lowered.
The oil passes through ducts (D) and (F), reaches the chamber (G) moving axially towards the en­
gine and the piston (4), which hqs helical teeth on the outside, is forced to rotate in a clockwise direc­
tion (seen from the timing side) on account of the above mentioned axial movement.
Its rotation is transmitted, by means of a straight toothed splining, to the pinion (5) which, bolted on­
to the threaded element of the camshaft (6), transmits the rotation to the shaft, altering the timing of
the inlet valves with an advance of 9°.
When the solenoid valve is de-energized, the valve body (2) returns to the initial position, interrupting
the flow of oil under pressure to the chamber (G), but allowing the return of oil to the drainage, thanks
to the force of the opposing spring (7).
An additiona duct guarantees the lubrication of the camshaft bearing even when the device is not acti­
vated.
The oil which reaches chamber (H) of the solenoid valve through seepage, is discharged through the
drainage duct (E).
Recovery
In the case of a problem with the solenoid valve, the final stage (driver) in the control unit is deactivated.
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