693 / 1236
ANTI LOCK BRAKING SYSTEM (ABS)
1
ANTI-LOCK
BRAKING
SYSTEM (ABS)
6.2.1 GENERAL INFORMATION
6
.2.1.1 NECESSITY 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 load sensing pressure valve
(LSPV) which limits the pressure to the rear axle to
give a front first locking sequence. The LSPV 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/she 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.
NOTE
ABS ECU calculates the Vehicle Speed and
Odometer signals. If ABS ECU fails vehicle speed
and odometer will not function.