Anti Lock Braking System for Commercial Vehicles

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„Cab“ - Version
Anti-Lock Braking System
for Commercial Vehicles
1st Edition
 Copyright WABCO 2006
Vehicle Control Systems
An American Standard Company
The right of amendment is reserved
Version 001/12.99(en)
8150100013 815 010 001 3

1 3
4. ABS / ASR
7. ANNEX 31
Contents ABS-D
1. Introduction
1. ABS-D Introduction
Anti-lock Braking Systems (ABS) or
- to use another common term - automatic
anti-lock systems - are used
to prevent a vehicle’s wheel from
locking as a result of excessive operation
of the service brake, especially
on a slippery road surface.
Thus lateral control on the wheels
being braked is maintained even at
full brake application or in panic
braking situations to ensure the cornering
stability and steerability of a
vehicle or a tractor-trailer combination
to the greatest possible physical
At the same time, the objective is to
optimize the utilization of the available
adhesion coefficient between
tyres and the road surface and thus
vehicle retardation and stopping distance.
High-performance ABS for commercial
vehicles was first introduced at
the end of 1981 by Mercedes-Benz
and WABCO after elementary systems
had been used in the USA
from the mid 70s.
System design and control principles
of this 4-channel system with
individual wheel control (4 sensors -
4 modulators, called 4S/4M below)
were subsequently highly successful
in the European market for commercial
vehicles and became the
basis for a world-wide standard for
all commercial vehicles with power
ABS and ASR have proved their value
as 4- and 6-channel systems in
commercial vehicles. The reliability
of systems and components from
series production is excellent, in
spite of their complexity. The demand
is rising not only in Germany
and Europe or Israel and Australia,
but also in the USA and in Japan.
As is generally known, the EEC and
other legal requirements demand
automatic anti-lock braking systems
for certain types of commercial vehicles.
It is these provisions and measures
which have resulted in the even
more widespread use of ABS and in
greater numbers being produced;
this in turn has allowed cost reductions
to be implemented, in spite of
keen competition. WABCO has now
developed the 4th generation of ABS
and ABS/ASR. The D-generation offers
different variants in the form of
modular system designs.
These are based on state-of-the-art
electronics technology with highperformance
micro computers, including
data storage, and take into
account recent diagnostic principles.
The 4- and 6-channel ABS/
ASR systems for commercial vehicles
offer various interfaces for
working together with electronic engine
control systems and the optimal
use of an integrated speed
limiting facility. Special functions for
both ABS and ASR operation are
available for selection in off-road operations.
This document describes the basic
elements and the operation, the design
and the system configurations
of these anti-lock systems for commercial
vehicles. The subject of
drive-slip control (ASR) is mentioned
only briefly in the section on
system functions.
In case of impending wheel lock, the
brake pressure of the corresponding
wheel will be decreased, held
during expected or measured wheel
re-acceleration and subsequently
increased in steps after re-acceleration.
The cycle is started again if the
brake force is still too high for the
actual friction level (adhesion).
Rear axle wheels are subject to individual
control (IR), front axle wheels
are subject to Modified Individual
Regulation (MIR).
Fig. 1 shows an example
of a control cycle
with the most important
control variables, wheel
deceleration threshold
-b, wheel acceleration
threshold +b and slip
thresholds λ1 and λ2.
As the...
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