SAFARI

ABS

ANTI-LOCK BRAKES

HOWABSWORKS

When the brake pedal is depressed, hydraulic pressure

is developed in the Tandem Master Cylinder, which is

used to actuate the brake (two in front and two in

rear).

The brake pipes are connected to the brakes through

the ABS Hydraulic unit.

They make two independent circuits vertically split.

The primary circuit connects the Front Left and Right

brakes while the secondary connects Rear brakes

through connectors.

Anti lock braking system ABS 5.3 is a 3-channel

vertical split system consists of an ECU attached

to hydraulic unit and 4 wheels speed sensors (one

at each wheel).

The ECU controls the hydraulic unit. Each front wheel

has one individual pair of inlet and outlet valves.

Both the rear wheels share one pair of inlet and

outlet valves.

Whenever ABS system recognizes incipient wheel

lock at one or more wheels, it ensures the stability

of wheel/ vehicle by modulating the brake pressure

in 3 phases which are, (1) Pressure hold (2) Pressure

decrease & (3) Pressure increase. The wheel speed

sensor sends alternating voltage signals to the

Electronic Control Unit (ECU). The ECU calculates

the vehicle reference speed every 10 msec.

From this data the ECU calculates the % slip when

the wheels are braked. When the % slip is above

the permissible limit (varies with tyre to road

traction), the ECU sends signal to the solenoid valves

in the HU to carry out pressure maintaining and

reduction phase.

When % slip recovers within limits, pressure is

increased to achieve optimum stopping distance.

When one or more wheels are about to lock due to

rapid deceleration, the ABS comes into action. It

modulates (holds or decreases, increases) the brake

pressure to avoid wheel lock.

The ABS 5.3 controls all the 3 channels (The ABS

controls the front wheels independently and the rear

wheels in tandem). The brake pressure required to

bring ABS into operation may vary depending upon

road surface and tyre adhesion. A dry pavement

surface requires a higher brake force than a slippery

surface to engage ABS.

The ABS comes into play when panic braking is applied

on the vehicle during emergency.

The driver feels

the effort of the ABS through the pulsating (up

and down movement) of the brake pedal and

audible noise in the brake system.

This is absolutely Normal. This should not be

interpreted as a fault in the brakes. On the

contrary it’s an indication that the ABS is

working.

This is an intentional warning to the driver that a

wheel or wheels are tending to lock up due to the

limit of tyre to road adhesion.

In this situation it is important to keep the brake

pedal depressed fully so that the ABS can

regulate the brake application.

On No account pump the brake pedal