Mitsubishi Eclipse. Technical Information Manual (1994) — part 64
A B S
ELECTRONIC CONTROL UNIT (ECU)
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The ABS-ECU detects the vehicle speed in
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terms of a signal from the wheel speed sensor
The ABS-ECU has diagnostic and
tions.
to determine the rotating condition of the wheel,
estimates the skidding condition of the wheel
If any failure is found by diagnostic test mode,
on the basis of the predetermined theory, and
the fail-safe function is activated and the ABS
outputs a signal to move the solenoid valve
warning light will illuminate.
in the HU in such a way as to prevent locking
the wheel.
BLOCK DIAGRAM
ABS-ECU
Battery
Stop light
switch
Generator
terminal L
Power
CPU II
.
monitor
Operation control,
. .
Sensor
interface
circuit
Motor relay
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monitor circuit
drive circuit
solenoid control,
.
snitor circuit
Valve relay
drive circuit
fail-safe
I
I interface circuit
FUNCTION OF INDIVIDUAL CIRCUITS
(1) The wheel speed sensor interface circuit converts the AC
voltage signal into DC pulse signal.
(2) The power monitor circuit, sensor interface circuit and motor
drive monitor interface circuit are electrical converters for
inputting the stop light switch and other vehicle condition
signals.
(3) The CPU I and II are microcomputers which perform wheel
speed, wheel deceleration and other calculations required
for anti-lock control on the basis of the wheel speed signals
input from the wheel speed sensors, and provides anti-lock
controls according to the calculated data. The two micro-
computers, CPU I and II, monitor each other to detect
a failure in the system.
They also have diagnostic test mode and failure detection
fail-safe functions.
(4) The solenoid drive circuit, motor relay drive circuit, valve
relay drive circuit and ABS warning light drive circuit are
electrical converters for ON/OFF control of the HU solenoid
valves to control the brake fluid pressure, and for ON/OFF
control of the motor for producing a high fluid pressure
in the HU, and also for lighting the warning light to alert
the driver to a system error.
(5) The failure code memory stores the codes of failures that
occurred in the system and does not clear the data even
if the battery power supply is disconnected.
DRIVE-CONTROL COMPONENTS ABS
EXPLANATION OF ECU CONTROL
Braking Hydraulic Pressure Control
The figure below shows the relation between the
wheel speed, wheel acceleration, control signal from
the ECU and braking hydraulic pressure.
The ECU uses the signal from each wheel speed
sensor to calculate wheel speed and wheel accelera-
tion, calculates suspected vehicle speed from these
and monitors the slipping of the wheels. If it seems
the wheels are about to lock during sudden braking,
a signal to reduce pressure or a signal to hold pres-
sure is sent to control wheel locking. On the other
hand, if the danger of the wheel locking disappears,
a signal to increase pressure is sent and the braking
Wheel speed
Wheel acceleration
Pressure reduction
Signal pressure
Pressure increase
Brake hydraulic
pressure
Control
The ABS for FWD is a
method
for independent control of the right and left front
hydraulic pressure is increased to normal master
cylinder pressure. Furthermore, in order to prevent
a sudden increase in hydraulic pressure at this time,
a pulse step control is performed to repeat the signal
to increase pressure and the signal to hold pressure.
By repeating this cycle and controlling the output
braking hydraulic pressure, the wheel is kept in a
narrow slipping ratio to assure the ideal braking
force. This hydraulic pressure control is applied inde-
pendently to the left front wheel, right front wheel
and both rear wheels.
Actual vehicle speed
--
- - -
- - - - -
Slip ratio set value
- - - - - - - _
_
_
_
control
Time
speed
wheels and select-low control of the rear wheels.
Control Speed
Brake pressure is controlled at a vehicle speed of
approximately 8 km/h (5 mph) or higher. When
speed falls below approximately 3 km/h (2
mph), control ends.
A B S
ABS MOTOR RELAY CONTROL
When a drive signal is output from the ABS-ECU
placed in the ON state to operate the pump motor.
to any of the solenoid valves, the motor relay is
ABS VALVE RELAY CONTROL
If the system is found O.K. after an initial check,
to supply power to the solenoid valves of the HU
the ABS valve relay is placed in the “ON” state
to prepare for operation of ABS.
Approx. 1
second
START
Ignition
switch
ACC,
LOCK
ABS Warning Light Control
In the following cases the ABS warning light lights up.
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If lights up when trouble in the system is recognized.
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It illuminates in the pattern shown in the figure on the
left when the ignition switch is turned ON, to check the
ABS warning light circuit.
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