Presssure increase phase

Presssure increase phase

1. Electronic control unit
2. Low-pressure accumulator (reservoir)
3. Recycling pump motor
4. Recycling pump
5. High-pressure accumulator (damping chamber)
6. Brake pump
7. Servo unit
8. Rapid pressure reducing valve
9. Inlet solenoid (A) open (B) closed
10. Outlet solenoid (A) closed (B) open
11. Brake caliper
12. Rpm sensor
13. Phonic wheel
14. Constriction

When the driver presses the brake pedal, the pressure generated by the brake pump (6) reaches the brake calipers without undergoing variations, as the solenoids (9) and (10) of the hydraulic unit are not earthed by the electronic control unit.

When the braking force increases, the wheel deceleration consequently increases: this causes faster deceleration of the car (i.e. the wheel slip increases).
The slip value must not exceed a particular value beyond which the wheel loses grip with the ground and begins to skid, resulting in loss of direction control and increase in braking distances.

The wheel speed sensor (12) indicates when deceleration values which could impair the wheel's grip on the ground are reached; at this point the electronic control unit (1) drives the solenoids on the electro-hydraulic control unit, reducing the braking force and allowing the wheel to increase its speed and so recover grip.