Chrysler Stratus RHD 1997 Interactive Electronic Service Manual page 175

5 - 80 BRAKES
DESCRIPTION AND OPERATION (Continued)
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.
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.
SYSTEM RELAY AND PUMP/ MOTOR RELAY BOX SYSTEM RELAY AND PUMP/MO- TOR RELAY BOX 10 WAY CON-
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. 3) 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. 3).
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.
Fig. 3 System Relay And Pump/Motor RelayBox
SYSTEM RELAY OPERATION
The main purpose of the system relay is to put the
ABS system into a stand-by mode for ABS operation.
The system relay is energized by the CAB shortly
after the ignition switch is turned on.
When energized by the CAB, the system relay
turns off the ABS warning lamp and provides 12
volts to the CAB. This voltage can then be used by
the CAB to energize the decay solenoids during ABS
braking. When energized, the system relay also pro-
vides the pump/motor relay coil with 12 volts. The
ground path to the pump/motor relay is completed by
the CAB during ABS braking.
Conversely, when the system relay is de-energized,
the ABS warning lamp is illuminated, voltage to the
decay solenoids is cut off, and the pump/motor relay
is prevented from energizing. Typically, the system
relay is de-energized by the controller when a fault is
detected that requires turning ABS off.
NECTOR 6–WAY NECTOR CON-
JA