Hydraulic Head; Cam Seal - Fiat Bravo Service Manual

Bravo-Brava

Hydraulic head

The functions of metering, pumping and distributing take place in the main section of the injection
pump, known as the hydraulic head.
The hydraulic head is composed of t w o groups:
- the hydraulic head stator;
- the distributor rotor, made up of a single element and t w o pumping pistons.
The distributor rotor is coupled w i t h the housing in the hydraulic head, whilst the pumping pistons are
coupled with the housings in the rotor. This means that these parts are not interchangeable w i t h others
but constitute a single assembly.
1. Roller
2. Roller carrier
3. Small piston

4. Cam seal

1. Cam seal
2. Cam seal bolt
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ft
TD 100
l x 9 6 " C i , n C t j l
The fuel subject to the transfer pressure en-
ters one of the ports in the hydraulic headl;
the opening of this port is controlled by the
movement of the metering valve connected
to the mechanical regulator.
During the charging cycle, t w o ports in the
rotor are aligned with two filling ports for the
head stator. A metered quantity of fuel, regu-
lated by the metering valve, enters the p u m p -
ing element and moves the pumping pistons
(3) away, pushing the group formed by the
roller (1) and the roller carrier (2) outwards.
By rotating the rotor interrupts the alignment
between the charging and filling ports (end
of charging cycle).
By continuing the rotation, one of the fuel
supply ports coincides with one of the high
pressure outlets.
Cam seal
The internal surface of the cam seal has lobes
(1) which are diametrically opposite and is
machined with precision.
The shape of the lobes causes the pressure
movement in the pump, determines the dura-
tion of the injection stage and standardizes
the supply cycles.
The cam seal bolt (2) connects the latter to
the injection advance adjustment system.
When the pump starts the injection cycle, the
t w o roller and roller carrier units w h i c h are in
contact with the pistons, start to move i n -
wards under the force of the t w o opposing
lobes.
This is the start of the injection.
Whilst the rotor continues to rotate, the
rollers move upwards, until they reach the
top of the lobes.
This marks the end of the injection.
Continuing the injeciton cycle, the rollers
lose contact with the cam seal and the hy-
draulic head rotor returns to the l o w pressure
condition ready for a new pressurizing cycle.
- - J l l l i
E n g i n e
Fuel system
10.
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