Decrease pressure phase (Brakes)

1. Master cylinder
2. Hydraulic modulator
3. Piston
4. Cut - off valve
5. Wheel Caliper
6. Speed sensors
7. ECU
8. Solenoid valve
9. Modulator reservoir
10. Pump
11. Accumulator
12. Pressure switch

Decrease pressure phase

If the force exerted on the brake pedal is sufficiently large to cause a potential wheel locking condition, the ECU sends a signal to the relevant solenoid valve directing pressure from the accumulator into chamber C of the modulator.

The high pressure forces the modulator piston upwards against the spring pressure in chamber D. The modulator cut - off valve closes preventing any further fluid pressure at the master cylinder being transmitted to the brake caliper. This is known as the maintain pressure phase. If by removing the pressure transmitted by the master cylinder to the brake caliper the potential wheel locking condition has receded, then the ECU operates the solenoid valve to relieve pressure from chamber C of the modulator, returning braking to normal.

If the potential wheel locking condition is still present, the pressure in chamber C is increased, the modulator piston moves further upwards increasing the volume of chamber B allowing fluid to flow from the brake caliper into the chamber, thereby reducing the pressure at the brake caliper. At the same time the volume of chamber A is