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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 additional flow of brake fluid is determined by the brake pressure in the master cylinder, which is in turn proportional to the pressure on the brake pedal. The brake pressure applied to the brake circuits is based on the decrease in speed sensed by the wheel sensors. The control unit regulates the inlet and outlet valves so that maximal braking force is transmitted between wheel and 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.