HCU (Hydraulic Control Unit): Operation: Notes

All switching components of the ABS system are combined in the ABS hydraulic unit. A 2/2-way valve for build-up/hold pressure or hold/reduce pressure functions is used on each wheel for control. At the rear, the same valves are used for both wheels. The return pump integrated in the hydraulic unit is used to return the brake fluid during the pressure reduction phase.

An increase in pressure compared to the pressure controlled by the master brake cylinder is not possible during the ABS control phase. A muffler is fitted for each brake circuit to reduce delivery noise. During the ABS pressure reduction phase, the brake fluid flows back to the return pumps via the low-pressure accumulators.