SAFARI

ANTI-LOCK BRAKES

ABS

4. ANTI LOCK BRAKE SYSTEM - THEORY

Anti lock Brake system (ABS) is a closed loop

system, which modulates the brake pressure in

response to the brake slip rate of the wheel so as to

prevent the controlled wheel or wheels from

becoming fully locked above a preset minimum

speed.

During emergency braking situations at high speeds,

panic braking will be applied under conditions like -

Un-anticipated obstacle and mistakes committed by

other drivers and pedestrians or braking under more

critical driving conditions such as driving on wet

and slippery road surfaces like ice etc the wheels

tends to lock which in turn will skid. This will lead to

loss of steerability and stability of the vehicle as it

loses traction.

Wheel slip :

The vehicle can stop in relation to how well the tyre

contact surface grips the road. At 0% slip, the tyre

rotates freely and at 100% slip, the tyre and wheel

are locked and the weight of the vehicle pushes the

locked tyres along the road surface. In this situation,

vehicle stability and steerability will be lost.

During gradual braking, the %slip will be in between

10 to 20% and at this condition vehicle stopping

distance and steering control will be at their best.

This optimum slip (10 to 20 %) is required for

achieving maximum braking performance & for

stopping the wheel.

The theory behind ABS is simple. Whenever a driver

brakes, the wheels of the vehicle have to transfer

this braking force to the ground surface for achieving

braking. As long as driver brakes gradually, the

braking force is transferred through the tyres to the

ground surface & optimum braking is achieved. But

when driver applies panic braking, the tyres will stop

rotating instantaneously (locking condition). The

vehicle drags all the 4 wheels in the same direction

(at the point of braking) & also driver cannot steer

the vehicle so as to avoid any accident.

To avoid the wheels from getting locked & skidding

while panic braking, Antilock brakes system is

provided. The main benefits of ABS are in the area

of vehicle stability and steerability. i.e. This system

prevents the wheel locking during emergency braking

situations and thereby helps the driver to maintain

: Stable Range

: Unstable range

1 : Dry Asphalt

2: Wet Concrete

3. Snow

4. Polished Ice

stability of the vehicle & also in bringing the vehicle

to a complete stop with a minimum possible stopping

distance in the safest possible way.

The purpose of ABS 5.3, 4-sensor 4-wheel, vertical

split system is to provide

Enhanced steering control by enabling the

vehicle to move in a driver’s intended direction,

even during panic braking.

Enhanced braking stability by making the most

of available traction on all surfaces.

It’s operational throughout the vehicles entire

speed range, effective down to the speed of

2.75 km/ h.

It is capable of rapid adaptation to changes in surface

traction. ( Dry road with patches of ice) and capable

of slowing down the yaw effect on the vehicle when

vehicle is driven on a µ split track, so that even an

average driver can initiate compensatory counter

steer.

ECU continually monitors the operating status of

ABS. Incase of ABS failure driver will be alerted

and conventional braking will still be operational

without ABS.

Fig. 3