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ABS modulation

ABS modulation



A. Speed

B. Braking force

C. Vehicle speed

D. Wheel rotation speed

E. Intake valve open, outlet valve closed

F. Intake valve closed, outlet valve open

G. Outlet valve open and return pump activated


When the electronic control module senses that a wheel is being retarded (speed decreasing) too much, it modulates the brake press in three phases.

Phase 1

The intake valve closes. This prevents an increase in brake pressure to the brake unit and allows brake fluid to accumulate in front of the intake valve for use in phase 3.

Phase 2

The outlet valve opens and also the passage from the brake unit to the pressure accumulator that can quickly take away the pressure from the brake unit. At the same moment that the outlet valve opens the control module starts the return pump which pumps the pressure back to the master cylinder. The wheel rotational speed will increase.

Phase 3

The outlet valve closes, the return pump stops and then the intake valve opens. This causes the wheel rotation speed to decrease.

Phase 1 to 3

Repeats until braking ceases or sufficient friction between the tyre and road surface is achieved. In case of open or short circuit the valves will resume their brakes off position, and braking action will be without ABS modulation.