ABS
ABS
is the abbreviation for anti-lock braking system (originally
from the German Antiblockiersystem). ABS is designed to prevent
locking of a vehicle’s wheels or excessive slip between the
tires and the road surface on braking;
as a result, it maintains the steerability and directional
stability of the wheels. It works on the principle that to
achieve the shortest stopping distance, all wheels need to
be almost but not quite on the point of locking. This is because
the rolling friction developed by a tire that is still exerting
a rotational grip against the road always exceeds the locked
wheel friction between the road
surface and a tire that is simply sliding over it, especially
when the surface is wet and slippery. Experienced drivers
know that the best manual braking technique under such conditions
is what is called cadence braking. ABS achieves an optimal
form of cadence braking through the use of three main components:
wheel speed sensors, an electronic
control unit, and a system modulator.
The wheel speed sensors constantly monitor wheel speeds, sending
this information (usually electronically) to the microprocessor-based
electronic control unit. The control unit detects any significant
deceleration of the wheels relative to the vehicle, which
could result in the braking force at any wheel becoming greater
than the adhesion force between tire and road. Typically,
the control unit can modulate the braking force between 3
and 12 times a second, depending on road conditions. The system
modulator receives commands from the electronic control unit
and translates them, independently of driver action, into
valve-based sequences that modulate the pressure in the individual
brake lines.
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