Hydraulic Unit

To control the braking system pressure, the brake hydraulic unit has a 3-way valve which permits 3 separate brake pressure conditions. Pressure build-up, pressure retention and pressure drop are the 3 pressure phases that adapt to the vehicle braking requirements. The control procedures are as follows.

As soon as wheel lock-up is indicated, brake fluid pressure is reduced. If the wheel still tends to lock, pressure will be further reduced until wheel acceleration or the slip limit is detected. The pressure is then raised and the control phases repeated. These pressure changes occur in milliseconds.

The return delivery pump returns brake fluid from the wheel brake cylinder, while dropping the pressure to the appropriate brake circuit. The pump is a 2-piston pump design so circuits of a dual brake circuit system remain separated.

Two relays are located under the cover of the hydraulic control unit: an engine relay and a valve relay. The engine relay is the larger relay.