Hydraulic Unit

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

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

1. As soon as wheel lock-up is indicated, brake fluid pressure is reduced. The return delivery pump returns brake fluid from wheel brake cylinder, while dropping pressure to appropriate brake circuit. The pump is a 2-piston pump design so circuits of dual brake circuit system remain separated.
2. If wheel still tends to lock, pressure will be further reduced until wheel acceleration or slip limit is detected.
3. Pressure is then raised and control phases repeated. Pressure changes occur in milliseconds.