SAFARI BSVI SERVICE MANUAL

BRAKES (EPB) 15 7. ABS 9 ELECTRONIC CONTROL UNIT / HYDRAULIC CONTROL UNIT (ECU / HCU): General 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 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. (ii) Hydraulic Control Unit (HCU) General: It consists of a Return Pumps, Solenoid Valves, Accumulator, and Motor. It forms the link between the TMC and the foundation brakes. It implements the commands is- sued by the ECU by using solenoid valves to control the pressure at the foundation brakes. There are four pairs (4-channel system) of Inlet and Outlet valves and are located in the upper section of the modulator. Solenoid valves are responsible for modulating the pressure in the brake cylinder during active ABS control. The Return Pump element is installed in the center of the modulator and is driven by an electric Motor. The pump transfers the brake fluid emerging from the wheel brakes through the accumulator on its way back to the TMC The pump actuation can be felt on the foot pedal as pulsations. Accumulator are Located in the lower section of the hydraulic modulator. The accumulator absorbs the surge in brake fluid that accompanies the pressure reduction phase.