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BRAKE SYSTEM
497
BRAKES
AUTO INCREMENTAL BRAKE
General:
For the drum brakes to function correctly, the brake
shoes must remain close to the drumwithout touching
it. If they get too far away from the drum (as the shoes
wear down, for instance), the piston will require more
fluid to travel that distance, and this will increase the
pedal travel. So to avoid this excess travel, drum
brakes are having an
automatic adjuster
which
ensures that, the gap between brake shoes and brake
drum remains constant. This gap is the distance
traveled by the brake shoe, when it comes in contact
with the brake drum.
Auto adjuster comprises of the strut assembly,
adjuster screw sub assembly and the rocker. The pawl
is attached in the strut assembly by spring force and
with offset leaf spring, engages with the adjustment
nut.
It provides optimal adjustment value of approximately
0.02 mm for every brake adjustment.
Working:
(a) Driving (non – braking) Mode:
The shoe return springs, upper and lower, pulls both
brake shoes together, away from brake drum. This
results in forcing the adjuster screw sub assembly
and the brake adjuster nut against the strut assembly
so that the rocker located between them can not move.
(b) Brake applied mode:
When the service brakes are applied, the wheel
cylinder pistons forces brake shoes against the brake
drum. This causes the adjuster bolt spring to pull the
adjuster screw sub assembly and the adjuster nut
away from the strut assembly, thus generating a gap
in which the rocker is free to move.
Rocker movement under leaf spring force causes pawl
to push tooth of adjuster nut. This results into rotation
of adjuster nut which expands adjuster screw sub
assembly. This restores gap between shoes and drum,
thereby maintaining it.