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Index Data Technology Repairs Car care Controls Overview
121n
Antilock Brake System (ABS)
The concept
ABS enhances active safety by helping
to prevent the wheels from locking
when the brakes are applied. This is
done because locked wheels are
dangerous. When the front wheels
slide, the driver loses steering control
over the vehicle. Traction loss at the
rear wheels can cause the rear axle to
break into an uncontrolled skid.
With ABS, the shortest possible braking
distances are achieved under most
conditions (on straight-aways and in
curves, with different road surfaces).
ABS is designed to meet two essential
requirements during every brake appli-
cation:
> To help provide vehicle stability
> To help maintain steering control and
maneuverability – on all types of road
surfaces (asphalt, concrete, mud,
wet, snow, ice).
Braking with ABS
The system becomes operative once
the vehicle exceeds a speed of approx.
6 mph (10 km/h). The ABS is deacti-
vated whenever the vehicle's speed
drops back below approx. 4 mph
(6 km/h). This means that the wheels
can lock in the final phase of a brake
application – a factor of no significance
in actual practice.
If you are in a situation that requires full
braking, you will exploit the full benefits
of the ABS system if you apply
maximum brake pressure ("panic
stop"). Since the vehicle maintains
steering responsiveness, you can avoid
possible obstacles with a minimum of
steering effort, despite the full brake
application.
The ABS system closed-loop control
circuit cycles in fractions of a second.
A pulsing of the brake pedal, combined
with the sounds associated with the
hydraulic controls, tells you that the
brake system is within its maximum
limit range and reminds you that you
should adapt your vehicle's speed to
road conditions.
On road surfaces which have a loose
layer on a firm base (on gravel or snow,
for instance), the braking distances with
ABS may be longer than with the
wheels locked. This is also true if snow
chains are mounted. However, ABS
continues to provide enhanced vehicle
stability and steering response under
these conditions.
Online Edition for Part No. 01 41 0 155 429 - © 09/00 BMW AG
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