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Index Data Technology Repairs Car care Controls Overview
143n
Antilock Brake System (ABS)
The concept
ABS enhances active safety by helping
to prevent the wheels from locking un-
der braking. The reason: locked wheels
are dangerous, because the vehicle
cannot be steered when the front
wheels slip, and loss of traction at the
rear wheels can cause the rear end to
break into an uncontrolled skid.
ABS is designed to meet two essential
requirements during every brake appli-
cation:
> To help provide vehicle stability.
> To help retain steering and maneu-
vering capability on all types of road
surface (asphalt, concrete, dirt,
moisture, snow and ice).
With ABS, the shortest possible braking
distances are achieved under most
conditions (on straight-aways and in
curves, with different road surfaces).
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 use.
The ABS system works best in situa-
tions requiring maximum pressure on
the pedal (full braking). Since the vehi-
cle maintains steering responsiveness,
you can nevertheless avoid possible
obstacles with a minimum of steering
effort.
The ABS closed-loop control circuit cy-
cles 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 also applies to
driving with snow chains. However,
ABS continues to provide enhanced
vehicle stability and steering response
under these conditions.
Online Edition for Part No. 01 41 0 155 420 - © 01/01 BMW Group
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