Stratus Sedan L4-2.4L VIN X (2003)
Hydraulic Control Assembly - Antilock Brakes: Description and Operation
Hydraulic Control Unit
The hydraulic control unit (HCU) contains the valve block assembly and pump motor assembly. The HCU and the CAB are mounted as an assembly
and are not separately serviceable.
Valve Block Assembly: The valve block assembly contains valves with four inlet valves and four outlet valves. The inlet valves are spring-loaded in
the open position and the outlet valves are spring loaded in the closed position. During an antilock stop, these valves are cycled to maintain the proper
slip ratio for each wheel. If the CAB detects slip, the inlet valve is closed to prevent any further pressure increase. If necessary, the outlet valve is
opened to release the pressure to the accumulators until the wheel is no longer slipping. Once the wheel is no longer slipping, the outlet valve is closed
and the inlet valve is opened to reapply pressure. If the wheel is decelerating within its predetermined limits (proper slip ratio), the inlet valve will
close to hold the pressure constant.
Pump Motor Assembly: The pump motor assembly provides the extra amount of fluid needed during antilock braking. The pump is supplied fluid that
is released to the accumulators when the outlet valve is opened during and antilock stop. The pump is also used to drain the accumulator circuits after
the antilock stop is complete. The pump is operated by an integral electric motor. This motor is controlled by the CAB. The CAB will turn on the
pump motor when an antilock stop is detected. The pump continues to run during the antilock stop and is turned off after the stop is complete. Under
some conditions, the pump/motor will run to drain the accumulators during the next drive off. The CAB monitors the pump motor operation internally.
