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ANTI LOCK BRAKING SYSTEM (ABS)
11
ANTI-LOCK
BRAKING
SYSTEM (ABS)
A. ABS ELECTRONIC CONTROL UNIT /
HYDRAULIC CONTROL UNIT
(ECU / HCU)
This is an Electro-hydraulic device for reducing,
holding and restoring pressure to one or more wheel
brake, independent of the brake pedal effort applied
by the driver.
It consists of:
(i) An Electronic Control Unit
(ECU)
and
(ii)
A Hydraulic Control Unit
(HCU).
(i) ECU
It is a solid state electronic device containing
computer functions, sensor signal processing
circuits, output device drives for the various ABS
valves and components and Failure Detection Logic.
The ECU is integrated in a single package with the
Hydraulic Control Unit
(HCU).
It has 2 Micro
controllers, which utilize the same program for
independent data processing and monitoring
functions. One of the Micro controllers has an
EEPROM to retain memory data in case battery
supply is interrupted. The EEPROM is a non-volatile
data storage device employed to store error codes,
which can be read out for diagnosis. When an error
is encountered ABS switches itself off and triggers
the ABS warning lamp. An independent module
controls the solenoid valve relay and return pump
motor.
ABS ECU senses the rotational speed of the wheels
and calculates the vehicle speed based on the signal
received from the wheel speed sensor. During
braking, deceleration will vary on pedal pressure, the
vehicle speed during braking, and the road surface
conditions. For example, deceleration rate will be
much higher on dry asphalt compared to wet or icy
surface.
ECU judges the slip condition between the wheel
and road surface by monitoring the change in
wheel’s rotational speed during braking. The ECU
controls the ABS actuator to deliver the optimum
hydraulic pressure to the brake cylinder to precisely
control the speed of the wheels, maintaining the
maximum brake force