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Braking with ABS modulation

Braking with ABS modulation


ABS modulation is activated when a wheel exhibits a tendency to lock up. The control module receives wheel-speed signals from a sensor at each of the wheels. If a wheel starts to lock up, the control module will modulate the brake force, i.e. the pressure in the brake lines, via the solenoid valves. The brake force is controlled individually for each wheel.

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 of the return brake-fluid flow is determined by the pressure in the master cylinder, which, in turn, is proportional to the pedal pressure. The brake pressure to the respective circuits is governed by the reduction in wheel speed signalled by the wheel sensors. The control module steers the operation of the inlet and outlet valves such that the maximum brake force is applied between the wheels and the road surface.

ABS modulation continues until either of the following conditions is true:


• 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.





Phase 1

Inlet and outlet valves closed

Phase 2

Inlet valve closed, outlet valve open and return pump activated

Phase 3

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