Chrysler 1997 Stratus Convertible RHD Service Manual page 169

SION CROSSMEM- FRONT DRIVESHAFT SUSPEN- BER
JX
DESCRIPTION AND OPERATION (Continued)
ABS BRAKES HYDRAULIC CONTROL UNIT (HCU)
WARNING: THE ONLY PARTS OF THE HYDRAULIC
CONTROL UNIT HCU THAT ARE SERVICEABLE
ARE THE RELAY BOX, THE PROPORTIONING
VALVES, AND THE HCU MOUNTING BRACKET. THE
REMAINING COMPONENTS OF THE HYDRAULIC
CONTROL UNIT HCU ARE NOT SERVICEABLE
ITEMS. NO ATTEMPT SHOULD EVER BE MADE TO
REMOVE OR SERVICE ANY OTHER PARTS OF THE
HYDRAULIC CONTROL UNIT HCU.
The hydraulic control unit HCU is located on the
right side of the vehicle, mounted to the front sus-
pension (Fig. 1). The HCU is mounted to the front
suspension crossmember using a mounting bracket
attached to the crossmember, which the HCU is
mounted to using 3 isolation bushings. The HCU con-
tains the following components for controlling brakes
during ABS braking: 4 Decay Valves, 4 Shuttle
Valves, 2 Fluid Sumps, a Pump/Motor and a relay
box. Also attached to the hydraulic control unit are
the rear brake proportioning valves and the vehicles
6 hydraulic brake tubes (Fig. 1).
Fig. 1 Hydraulic Control Unit Mounting Location
HYDRAULIC CONTROL UNIT DECAY SOLENOIDS
There are 4 decay solenoids, one for each wheel. In
the released position they provide a fluid path from
the master cylinder to the wheel brakes of the vehi-
cle. In the actuated (decay) position, they provide a
fluid path from wheel brakes of the vehicle to the
sumps. The Decay solenoids are spring loaded in the
released (build) position during normal braking.
HYDRAULIC CONTROL UNIT SHUTTLE VALVES
There are 4 Shuttle Valves, one for each wheel.
The Shuttle Valve is a hydraulically actuated valve
which shuttles when the decay solenoid and pump
are energized. This places an orifice (restriction) in
the line between the pump and the decay solenoid.
RIGHT FRAME RAIL STEERING GEAR HCU MOUNTING CONTROL UNIT HYDRAULIC BRACKET
This restriction provides a controlled build rate to
each wheel brake during an ABS stop. The Shuttle
Valve will remain in the orificed position until the
ABS cycle is complete. When the ABS cycle has been
completed the decay solenoids will return to their
released position which will equalize the pressure
across the Shuttle Valves. When the pressure equal-
izes, the spring loaded Shuttle Orifice valves will
return to the unrestricted position.
HYDRAULIC CONTROL UNIT FLUID SUMPS
There are two fluid sumps in the hydraulic control
unit (HCU), one each for the primary and secondary
hydraulic circuits. The fluid sumps temporarily store
brake fluid that is decayed from the wheel brakes
during an ABS cycle. This fluid is then delivered to
the pump to provide build pressure. The typical pres-
sure in the sumps is 50 psi, during ABS operation
only.
HYDRAULIC CONTROL UNIT PUMP MOTOR
ASSEMBLY
The HCU contains 2 Pump Assemblies, one each
for the primary and secondary hydraulic circuits.
Both pumps are driven by a common electric motor
which is part of the HCU. The pumps pick up fluid
from the sumps to supply build pressure to the
brakes during an ABS stop. The motor only runs dur-
ing an ABS stop and is controlled by the CAB via the
Pump/Motor Relay. The Pump/Motor Assembly is not
a serviceable item. If it requires service the HCU
must be replaced.
RELAY BOX
ABX-4 utilizes two relays contained in a relay box
mounted to the HCU. The relay box contains a sys-
tem relay and a pump/motor relay. A single 10-way
connector provides the electrical interface. The relay
box is serviceable as an assembly.
PUMP/MOTOR RELAY OPERATION
Pump/Motor power is supplied by the Pump/Motor
Relay. The pump motor relay is also part of the relay
box (Fig. 2) mounted to the HCU. If pump/motor
relay replacement is required, it is also only serviced
by the replacement of the relay box assembly (Fig. 2).
Voltage for the 12 volt side of the relay coil is pro-
vided by the system relay. The ground path through
the relay coil is completed by the CAB during ABS
braking. The relay contacts are closed when the relay
is energized. This provides 12 volts to the pump/mo-
tor as needed during ABS braking.
SYSTEM RELAY OPERATION
The main purpose of the system relay is to put the
ABS system into a stand-by mode for ABS operation.
BRAKES 5 - 67