Fiat 1995 Brava, Service Manual

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Bravo-Brava
B r a k i n g s y s t e m
Anti-lock braking system
33.
Pressure reduction phase
P4A17AO01
1. Electronic control unit 8. Rapid pressure reducing valve
2. Low-pressure accumulator (reservoir) 9. Inlet solenoid (A) open (B) closed
3. Recycling pump motor 10. Outlet solenoid (A) closed (B) open
4. Recycling pump 11. Brake caliper
5. High-pressure accumulator (damping 12. Rpm sensor
chamber) 13. Phonic wheel
6. Brake pump 14. Constriction
7. Servo unit
The electronic control unit (1) detects the wheel's tendency to lock and activates the* electrohydraulic
unit to limit the wheel deceleration to within the permitted threshold values.
The electronic control unit (1) earths the inlet solenoid (9) and outlet solenoid (10).
The inlet solenoid (9) remains closed, maintaining the break in connection between brake pump (6) and
brake caliper (11); the outlet solenoid (10) opens thus hydraulically connecting the brake caliper (11)
to the low-pressure accumulator (2) and recycling pump (4), in order to remove some of the fluid from
the brake caliper (11) and reduce the pressure on that caliper.
At the same time the electronic control unit (1) supplies the motor (3) for driving the recycling pump (4)
which returns fluid removed from the brake caliper (11) into the main circuit. The accumulator (2) or
low pressure reservoir present in the circuit stores some of the brake fluid removed from the calipers.
Through the circuit of the recycling pump (4), the brake fluid is drawn in and sent, through the damping
chamber (5) and constriction (14), into the main circuit of the brake pump (6). During this phase, a se-
ries of pressure waves (or hydraulic thrusts) is generated, and these are attenuated by the presence of
the damping chamber (5) and constriction (14). During this phase, because of the reduction in the
braking force, the wheel tends to assume the reference speed calculated by the electronic control unit
(1)-
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