Principle of Operation: Abs

The four ABS wheel sensors supply information to the ABS control unit that monitors the rotational speed of each wheel. Should one or more wheels decelerate at a rate that exceeds a predetermined value, the ABS control unit activates the ABS hydraulic unit and in turn reduces the hydraulic brake pressure supplied to the affected wheel(s). The ABS control unit and hydraulic unit are assembled together as a single unit.

When the control unit determines that ABS operation is required, it energizes the inlet and outlet solenoid valves within the hydraulic unit corresponding to the relevant hydraulic brake lines and starts the return pump. The inlet valve closes to isolate the brake line(s) from master cylinder pressure and the outlet valve opens to release pressure from the brake line into the accumulator. Thus the brake is released and the relevant wheel begins to accelerate. The control unit then opens and closes the inlet and outlet valves as necessary to modulate the hydraulic pressure and achieve the maximum possible braking effort without locking the wheel.

The return pump takes its fluid supply from the master cylinder reservoir and maintains pressure behind the inlet valves so that when the inlet valves re-open, the pressure in the brake lines is quickly re-established.

During anti-lock brake operation the driver will experience feed-back' in the form of a pulsating brake pedal that is accompanied by solenoid/pump noise.

Sub-systems of the ABS system are:

These Sub-systems are also included in the ASC and DSC Systems.