Braking Mode Hydraulic Circuit Component Function

SOLENOID AND VALVE FUNCTION
Through the following operation descriptions the function of the various hydraulic control valves in the ABS system will be described. The fluid control valves mentioned below, control the flow of pressurized brake fluid to the wheel brakes during the different modes of ABS braking.

NOTE: For explanation purposes we will assume all speed sensors are sending the same when speed information, requiring the same hydraulic fluid modulation at the same rate.

NORMAL BRAKING BUILD/DECAY VALVE FUNCTION BUILD/DECAY VALVES OPEN
The Brake Pedal is applied. The travel of the Brake Pedal closes primary and secondary circuits from the Master Cylinder fluid supply. Brake fluid from the primary and secondary circuits flows through the build/Decay Valves to the wheel brakes.

ABS BRAKING-DECAY MODE-DECAY SOLENOID FUNCTION DECAY SOLENOID ENERGIZED
This will allow brake hydraulic pressure to be dumped to the Hydraulic Control Unit (HCU) sump. At the HCU sump, the brake hydraulic fluid is picked up by the pump and restored to high pressure for the next build cycle.

ABS BRAKING-BUILD MODE-DECAY SOLENOID FUNCTION DECAY SOLENOID DE-ENERGIZED
Decayed brake fluid, is picked up by the pump in the HCU and restored to high pressure. This high pressure brake fluid causes the Shuttle Valve in the HCU to actuate, routing high pressure brake fluid through the build orifice. Routing the high pressure brake fluid through the build orifice allows for a controlled build pressure in the brakes hydraulic system. High pressure brake fluid from the build orifice then passes through the de-energized Decay Solenoid and to the wheel brakes to restore braking pressure.