Caravan FWD L4-2.4L VIN X (1997)
Hydraulic Control Assembly - Antilock Brakes: Description and Operation
Valves and Solenoids
INLET VALVES AND SOLENOIDS
There are four inlet solenoids, one for each wheel. In the released position they provide a fluid path from the master cylinder to the wheel brakes
of the vehicle. When the ABS cycle has been completed the inlet solenoids will return to their released (open) position.
OUTLET VALVES AND SOLENOIDS
There are four outlet solenoids, one for each wheel. In the released position they are closed to allow for normal braking. In the actuated (open)
position, they provide a fluid path from the wheel brakes of the vehicle to the Hydraulic Control Unit (HCU) accumulators and pump motor. The
outlet solenoids are spring loaded in the released (closed) position during normal braking.
SPECIAL VALVES (ABS WITH TRACTION CONTROL ONLY)
On vehicles that are equipped with ABS and traction control there are two special valves located in the valve block of the HCU. The special valves
are a normally open type valve and are solenoid actuated. The special valves are used to isolate the front brakes of the vehicle from the master
cylinder when the traction control system is operational. The front brakes need to be isolated from the master cylinder when traction control is
activated so that the HCU can build the required hydraulic pressure to the front brakes.
HYDRAULIC CIRCUITS AND VALVE OPERATION
Throughout the following operation descriptions, the function of the various hydraulic control valves in the ABS will be outlined. The fluid control
valves mentioned below control the flow of pressurized brake fluid to the wheel brakes during the different modes of ABS braking. For
explanation purposes, all wheel speed sensors except the right front are sending the same wheel speed information. The following diagrams show
only the right front wheel in a antilock braking condition.
Normal Braking Hydraulic Control
Normal Braking (Inlet/Outlet Valve And Solenoid Function)
(De-Energized) - 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 inlet valves to the wheel brakes.
ABS Braking Decay Mode (Outlet And Inlet Solenoid And Valve Function)
(Outlet Energized) - This energized outlet solenoid will allow brake hydraulic pressure to be dumped to the Hydraulic Control Unit (HCU)
accumulators. At the HCU accumulators, the brake hydraulic fluid is picked up by the pump and restored to high pressure for the next build cycle.
Also, the inlet solenoid is energized. This stops additional brake fluid from entering the wheel brakes from the master cylinder.
