BRAKES 18 10.ABS COMPONENTS A. ABS 9 ELECTRONIC CONTROL UNIT / HYDRAULIC CONTROL UNIT (ECU / HCU): This is an Electro-hydraulic device for reducing, holding & 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: Solid state electronic device containing computer functions, sensor signal processing circuits, output device drives for the various ABS valves & 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 nonvolatile 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.
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