HEXA

Anti-lock Braking System(ABS)

1. GENERAL INFORMATION :

A. NECCESSITY OF ABS WITH EBD :

Whenever the brakes are applied, the road

wheels transmit this braking force to the road

surface. To achieve optimal deceleration each

wheel should be braked to the point of imminent

lock. In this manner maximum possible braking

force would be imparted to the road surface.

However if a wheel is braked beyond this level it

will lock which can result in the vehicle skidding

and the driver loosing control.

EBD :

During normal braking there is always a level of

load transfer from the rear axle to the front. Due to

this occurrence it is necessary to ensure that the

rear axle wheels do not reach the point of lock

before the front axle wheels.

On vehicles without ABS and EBD this is

achieved through the use of a pressure conscious

regulating valve (PCRV) which limits the pressure

to the rear axle to give a front first locking

sequence. The PCRV allows only a

predetermined pressure to the rear wheels to

avoid locking of the rear axle wheels before the

front axle wheels. As a mechanical fixed ratio

component it cannot adapt to the condition of the

vehicle brakes, tyres, road or the vehicle load

conditions, and hence it cannot achieve ideal

braking at the rear axle

To enable optimum braking at the rear axle while

maintaining vehicle stability during braking, EBD

is provided. It enables the distribution of brake

force between the front and rear axle brakes to be

adjusted at any point of time, depending on the

condition of the vehicle brakes, tyres; the road, or

vehicle load conditions.

In the case of EBD failure the driver will be alerted

.It is unsafe to drive the vehicle with EBD not

working.

ABS :

In emergency braking conditions and when driving

on wet or slippery road surfaces like snow and

Ice, gravel, steel plates and bridges etc.., it is

possible that the braking forces at the wheel

exceed those possible to transmit to the road

surface. This will result in wheel locking (stopping

rotating). If one or more wheels lock under braking

the vehicle can go into a skid and no longer be

controlled by the driver as he will have lost

steerability.

To avoid the wheels from locking and prevent the

vehicle from skidding ABS is provided. It prevents

the wheels from locking and maintains the

steerability of the vehicle thereby helping the

driver to maintain stability of the vehicle while

bringing it to a stop in the safest possible way.

In case of ABS failures the driver will be alerted

and the conventional braking circuit will still be

operational.

ENGINE DRAG CONTROL (EDC) :

Engine braking is an act of using engine

compression as braking force instead of service

brakes. This is done when prolonged and

continuous brakes have to be applied. The

efficiency of the service brakes reduces in such

applications as they are subjected to high

temperatures. In such situations engine braking is

preferred as engine has a system to dissipate the

heat generated.

During such braking the vehicle will be running in

gear such that the wheels are connected to the

engine. Hence there are chances that the engine

may get stalled if the speed is very less resulting

in the drive wheels getting locked. EDC avoids

such situation by slightly increasing the engine

torque to avoid engine stalling and thus avoids the

wheel slipping.

In case of EDC failure the ABS will still be

working.

Cornering Stability Control(CSC) :

CSC Stabilizes the vehicle in bends by pressure

reduction at the inner wheels during partial

braking, Countermeasure to ensure stability while

braking in curves.

Rough Road ABS :

With rough Road ABS mode Special Braking

performance is offered to support Rough road

surfaces as compared to other drive modes. The

braking interval is increased and will cause

wheels lock up in a controlled manner so that

small wedges of material from the ground (such

as gravel or sand) build up in front of each wheel.

This can substantially reduce the stopping

distance of the vehicle.

NOTE :



ABS ECU in all the variants of vehicle

calculates the Vehicle Speed and Odometer

signals. If ABS ECU fails or CAN bus fails

vehicle speed and odometer will not function.



In all the 4x4 variants of vehicle ABS ECU

interacts and controls the TOD functionality. If

the ABS communication with TOD ECU is

lost, standard ABS functions shall continue

operating normally unless there is no other

fault.



If Rough Road ABS switch fails ABS mode

will shift to default mode and ABS functions

shall continue operating normally unless there

is no other fault in the system.