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.