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BRAKES
10
5. NECESSITY OF ABS with EBD
Whenever the brakes are applied, the Vehicle
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 be-yond this level it
will lock which can result in the vehicle skidding
and the driver losing control.
EBD:
During normal braking there is always a level of
load transfer from the rear axle to the front. During
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, tires or to the
road or vehicle load conditions, and hence it
cannot achieve ideal braking at the rear axel
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 throughout the vehicle life, irrespective of
the condition of the vehicle brakes, tires; or to the
road, vehicle load conditions.
In the case of EBD failure, the driver will be
alerted.
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 wheel locking limits. This will result in
wheel locking (stopping rotating). If one or more
wheels locks during braking, the vehicle can go
into a skid and no longer be controlled by the drive
as he will have lost steer ability.
To avoid the wheels from locking and prevent the
vehicle from skidding ABS is provided. It prevents
the wheels from locking and maintains the steer-
ability 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 the case of ABS failures, the driver will be
alerted and the conventional braking circuit will still
be operational.
6. VACUUM BRAKE BOOSTER
General:
Vehicle is equipped with a mechanical vacuum
booster to assist driver’s pedal effort. This is
achieved by using vacuum from engine inlet
manifold (for petrol engines) or vacuum pump (for
diesel engines). A diaphragm is provided between
the two shells of the booster, the difference of
pressure on two sides of diaphragm (one side
vacuum and another side atmospheric pressure)
gives mechanical advantage. This amplifies the
driver’s pedal effort while braking.
The unit is connected to the brake pedal and the
master cylinder. The vacuum booster input push
rod is connected to brake pedal while the output
push rod operates the master cylinder. If failure of
vacuum occurs, the two push rods act as a single
rod and the brakes will work in the conventional
manner, but more pedal effort will be required and
the fatigue of the driver will increase.
NOTE:
The booster assembly and TMC assembly are
coupled with the help of fasteners. The mating
dimensions of booster and TMC are factory set
hence:
1. Do not alter the height of the output rod of the
vacuum booster unit at any stage and ensure
booster output rod is correctly aligned to the
primary piston bore during assembly of TMC to the
booster.
2. Once the booster assembly is removed from
vehicle, at the time of refitting on vehicle, the
gasket at the mounting face of the booster should
be replaced with a new one.
3. Booster assembly is a non-serviceable unit and
it should never be tampered with.