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Braking with ABS modulation

Braking with ABS modulation


ABS modulation is activated when one or more wheels exceed the permissible slip threshold. The control module receives wheel-speed signals from a sensor on each wheel. If the slip threshold is exceeded, the control module will modulate the braking force, i.e. the pressure in the brake lines, by means of the solenoid valves. The braking force is controlled individually for each wheel.

The brake pressure to each brake circuit is governed by the reduction in wheel speed sensed by the wheel sensors. The control module controls the inlet and outlet valves in such a way that the greatest possible brake force is applied between the wheels and the road surface.

Pressure is retained when the inlet valve is closed and reduced when the outlet valve is opened at the same time as the return pump starts.

ABS modulation will continue until:


• The car has been brought to a standstill.

• The driver has reduced the pressure applied to the brake pedal such that the road surface is able to take up the brake force without any of the wheels tending to lock up.


The return pump, which returns excess brake fluid to the master cylinder, is activated only when the ABS mode is operative and the outlet valve is open.

The pressure in the flow of additional brake fluid is determined by the brake pressure in the master cylinder, which is in turn proportional to the pedal force applied.




Phase 1 Pressure holding

Inlet and outlet valves closed.

Phase 2 Pressure reduction

Inlet valve closed, outlet valve open and return pump activated.

Phase 3 Pressure build-up

Inlet valve closed, outlet valve open and return pump idle.