SAFARI

ABS

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 :

Control Unit (ECU along with EBD program)

Hydraulic Pressure Modulator

Wheel Speed Sensors (front & rear, 1 per wheel)

Acceleration Sensor

Red warning lamp on the control panel, which

stays on continuously in case of ABS failure.

Diagnostic socket for tester.

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

/ grip surface, the pressure corresponding

to that wheel is maintained on the high

/ 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.