SAFARI

ABS 18 ANTI-LOCK BRAKES 5. COMPONENTS OF BOSCH ABS 5.3 SYSTEM ABS for Safari is Robert Bosch ABS 5.3, 3-channel system suitable for Parallel (Vertical) split brake configuration. It consists of following components : l Control Unit (ECU along with EBD program) l Hydraulic Pressure Modulator l Wheel Speed Sensors (front & rear, 1 per wheel) l Acceleration Sensor l Red warning lamp on the control panel, which stays on continuously in case of ABS failure. l Diagnostic socket for tester. l EBD warning lamp which is same as parking brake lamp. Electronic Control Unit (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 Unit (HU). 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. This module supplies a stabilized voltage, monitors micro controller operations and triggers the ABS lamp in response to malfunction. Brake Pressure / Hydraulic Modulator An Electro-hydraulic device for reducing, holding & restoring pressure to one or more wheel cylinders, independent of the brake pedal effort applied by the driver. It consists of a Return Pump, Solenoid Valves, Damping Chamber, Accumulator, Non-Return Valve and Motor. It forms the link between the TMC and the foundation brakes. It implements the commands issued by the ECU by using solenoid valves to control the pressure at the foundation brakes. Fig. 9 There are three pairs (3-channel system) of Inlet and Outlet valves are located in the upper section of the modulator. Solenoid valves that are responsible for modulating the pressure in the brake cylinder during active ABS control. Each front wheel has one individual pair of inlet and outlet valves. Both the rear wheels share one pair of inlet and outlet valves. Incase one of the rear wheels is on low m / grip surface, the pressure corresponding to that wheel is maintained on the high m / grip surface also to prevent wheel locking due to limited slip differential. 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 through damping chamber. The pump actuation can be felt on the foot pedal as pulsations. In order to prevent damage to the TMC primary seals from the compensating port, the design of TMC is changed to central valve type (CV/CV) Accumulator and Damping Chambers are Located in the lower section of the hydraulic modulator. The accumulator absorbs the surge in brake fluid that accompanies the pressure reduction phase. The Damping Chamber suppresses pressure oscillations within the hydraulic system, preventing them from being propagated back to the brake pedal and reduces noise levels in the system.