EBS (EPB)-

Electronically
Controlled
Braking System

Description of System and

Functions

1998 Edition

 Copyright WABCO 1998

WABCO
Fahrzeugbremsen

A Division of
WABCO Standard GmbH

The right of amendment is reserved

EBS Table of Contents

Introduction ............................................................... 3

Benefits of EBS ......................................................... 3

System Design ................................................... 6 / 34

Description of Components..................................... 7
Brake Signal Transmitter ....................................... 7
Central Module ...................................................... 9
Proportional Relay Valve ..................................... 10
Backup Valve....................................................... 12
Axle Modulator..................................................... 14
Trailer Control Valve ............................................16
Other Components .............................................. 17

Description of a 4S/4M System.............................. 18

Function of Electro-Pneumatic Portion
of the System....................................................... 18
Electrical/Electronic Circuits ................................ 20
Control Functions................................................. 21
Supporting Functions........................................... 22

Error Detection........................................................ 23

EBS „Emergency Operations“............................... 24

Testing the EBS ...................................................... 25

Operation and Dials ................................................ 26

Error Code Description .......................................... 27

Diagnosis................................................................. 28
Diagnostic Controller ........................................... 28
Program Description ............................................29
Using the Diagnostic Controller ........................... 30
Using a PC........................................................... 33

Function scheme ...................................................... 35

2 WABCO
 Introduction / Benefits of EBS EBS

Preface Introduction
Comments on the publication “EBS - Electronically Increasing competition in the transport trade has also
controlled Braking System, Description of System and caused the requirements for braking systems to be
Functions 815 000 262 3“. increased steadily. The introduction of the Electronically
controlled Braking System EBS is the logical step to
EBS enhances vehicle and road safety by means of meet this and other requirements. EBS permits perpetual
reducing the stopping distance, achieving improved optimized balancing of the braking forces among the
braking stability and montitoring the braking system. In individual wheel brakes, and of the towing vehicle and its
addition, EBS considerably improves both economic trailer.
efficiency and driving comfort.
The comprehensive diagnostic and monitoring functions
For this reason, EBS will be included in new vehicle of the Electronically controlled Braking System are one of
series, the pioneer being ACTROS from Daimler-Benz the basic requirements for effective fleet logistics.
which has an electronically controlled air braking system
fitted as standard equipment. This system by name of
“Telligent® Braking System“ from Daimler-Benz
(formerly EPB), is a joint development by Daimler-Benz
and WABCO.
Benefits of EBS
Please note:
The term “Telligent® Braking System“ comprises the EBS Effectively Reduces Maintenance Costs.
whole of the braking system, not only its controlling
system which we call EPB. n EBS combines a large number of functions. The
objective is to reduce maintenance costs whilst
The ACTROS “Telligent® Braking System“ contains maximizing braking safety, e.g. by minimizing
some specific Daimler-Benz features for which WABCO, lining wear of the wheel brakes.
in applications for vehicles from other manufacturers,
has substituted its own solutions. These include the n Individual control according to the wear criteria on
following functions described in the publication in more both front and rear axles harmonizes lining wear.
detail: By evenly spreading the load across all wheel
brakes, total wear is minimized. In addition,
n redundancy valve, rear axle redundancy maintenance and lining change intervals coincide.
Laidup costs are drastically reduced.
n special control functions in the area of brake force
distribution (differential, drive-slip control DSR), n Depending on the vehicle’s service profile and
lining wear control and trailer control other factors, the vehicle owner achieves
considerable savings. A comparison of
n testing and diagnostic methods typical for maintenance costs for the braking system and the
ACTROS. foundation brakes for a tractor-trailer combination
using EBS versus a combination with a modern
conventional braking system shows high savings
for the first vehicle owner.

WABCO 2 3
EBS Benefits of EBS

EBS Ensures Compatibility

Between Tractor and Trailer - At Any Time

The harmonization of the braking processes for the EBS will recognize any incompatibility between the
whole of the tractor-trailer combination, especially if towing vehicle and its trailer, harmonizing the braking
combinations are varied frequently, can often not be performance. If the brakes work at their best possible
achieved satisfactorily by conventional means. operating point, this not only optimizes maintenance
costs for the brakes but also provides a maximum in
Improper balancing, e.g. if a trailer is not braked safety and comfort.
effectively enough, will cause uneven lining wear.

Comprehensive Diagnostic Facilities

One basic requirement for effective fleet logistics are EBS monitors both all essential components and the
low-maintenance systems. EBS provides the vehicle braking system’s functions. Any defects are recognized
owner with up-to-date information on the state of his by the system and accurately displayed for maintenance.
braking system and the foundation brakes. This permits The maintenance specialist can then rectify the error in
anticipated maintenance scheduling. question.

4 WABCO
 Benefits of EBS EBS

Increasing Braking Safety

When developing EBS, WABCO did not merely take its For this reason, a vehicle fitted with EBS is capable of
bearings from the applicable legal requirements. Next to much more than what is legally required.
the benefit for the user, it is safety which takes priority.

conventional
braking system

EBS
speed

stopping distance

The High Degree Of Safety Through ABS Is

Achieved By Several Factors:

n Shorter response and pressure buildup times for n Constant monitoring of the service brake and its
the brakes on front and rear axles and trailer axles components. In the event of the performance of
n Improved ABS function
the wheel brakes being reduced, this will be
recognized by the EBS, and the driver is alerted.
n Towing vehicle / trailer properly balanced at all
n Integrated ASR function provides optimized
times
vehicle stability and traction when moving off.

WABCO 2 5
EBS System Design

Modular Design of WABCO EBS

The configuration and the structure of WABCO’s EBS For meeting the essential requirements of the vehicle
permits a high degree of flexibility for the vehicle owner, WABCO recommends an EBS which comprises
manufacturer when designing the system. For this individual pressure control on front and rear axles and
reason, the most varied of needs can be met: trailer control, and which provides for pneumatic
redundancies in all braking circuits.
n partial or full system
n type of redundancy
n trailer control strategy
n elecrical interfaces
n etc.

2P/1E-EBS

AM = Axle Modulator
TCV = Trailer Control Valve
BST = Brake Signal Transmitter
PRV = Proportional Relay Valve
BV = Backup Valve
S = Speed Sensor
W = Wear Sensor

This EBS consists of a dual circuit and an overriding trailer control valve.
single-circuit electro-pneumatic circuit. This An expansion of this configuration by an additional axle
configuration is described as 2P/1E-EBS. modulator for the rear axles would then provide a
The single circuit electro-pneumatic part of the system 6-channel EBS.
consists of one central electronic control unit (central The structure of the subordinate dual-circuit pneumatic
module), the axle modulator with integrated electronics part of the system is basically identical with that of a
for the rear axle, a brake signal transmitter with parely conventional braking circuit. This part of the system
pneumatical integrated stroke sensors and brake serves as a backup and becomes effective only if the
switches, an electro-pneumatic control valve and two electro-pneumatic circuit fails.
ABS valves for the front axle, plus an electro-pneumatic

6 WABCO
 Description of Components EBS

Brake Signal Transmitter 480 001 ... 0

The brake signal transmitter is used to generate
electrical and pneumatic signals to apply to, or release
pressure from, the Electronically controlled Braking
System (EBS). This unit is designed for two pneumatic
and electrical circuits respectively. Commencement of
actuation is electrically recorded. A sensor reads the
travel of the actuating pin which is then, after modulation
of its pulse width, transmitted as an electrical signal. In
addition, there is an output of the pneumatic backup
pressures in Circuits 1 and 2. In this process, the
pressure of the 2nd circuit is retained slightly. Optional:
Via an additional control port, the pneumatic
characteristic of the 2nd circuit can be modified.

Position (MB Actros): Driver’s cab - front

Installation location: similar to previous brake valve

WABCO 2 7
EBS Description of Components

Brake Signal Transmitter 480 001 ... 0

Function

Central Module
Backup Valve

Air Reservoir

Proportional
Relay Valve

Air Reservoir

8 WABCO
 Description of Components EBS

Central Module 446 130 ... 0

The central module is used to control and monitor the
Electronically controlled Braking System. From the signal
received from the brake signal transmitter it determines
the vehicle’s intended retardation. Together with the
wheel speeds measured by the wheel speed sensors,
the intended retardation is the input signal for EBS
control which uses these readings to establish the index
pressure values for the front and rear axles and the trailer
control valve. The index pressure for the front axle is
compared with the actual value taken, and any
differences are balanced by means of the proportional
relay valve. Output of the trailer control pressure is Installation location (MB Actros):
achieved in a similar manner. In addition, the wheel foot space - passenger side
speeds are evaluated to commence ABS control by
modulating the brake pressures in the brake cylinders in
the event of the wheels showing a tendency to lock. The
central module exchanges data, via the EBS system bus,
with the axle modulator (or axle modulators in 6S/6M
systems). Electrical braking systems for trailers are
actuated via a data interface to ISO 11992. The central
module communicates with other systems of the towing
vehicle (engine control, retarder, etc.) via a vehicle data
bus.

WABCO 9
EBS Description of Components

Proportional Relay Valve 480 202 ... 0

In the Electronically controlled Braking System, the
proportional relay valve is used as an actuator for the
output of brake pressures at the front axle.

It consists of a proportional solenoid valve, a relay valve

and a pressure sensor. Electrical actuation and
monitoring are effected by the central module of the
hybrid system.

The control current determined by the electronics is

converted by the proportional relay valve into control
pressure for the relay valve. The output pressure of the
proportional relay valve is proportional to that pressure.
The pneumatic actuation of the relay valve is effected by
the redundant pressure of the brake signal transmitter.

Installation location (MB Actros):

front shock absorber area - left

10 WABCO
 Description of Components EBS

Proportional Relay Valve 480 202 ... 0

Function

Brake Signal
Transmitter Central Module

Air Reservoir

Air Reservoir
Brake Chamber
Front Axle

Rear Axle

WABCO 11
EBS Description of Components

Backup Valve 480 205 ... 0

The backup valve is used to rapidly increase or decrease
the pressure for the brake cylinders on the rear axle in
the case of a backup; it consists of several valve units
which have to perform the following functions, among
others:

n 3/2-way valve to prevent backup operation if the

electro-pneumatic braking circuit is not defective
n relay valve function for improving the time
response of the backup
n pressure retention in order to synchronize the
commencement of pressure output on the front
and rear axles in the event of a backup
n pressure reduction to avoid overbraking of the rear
axle to the largest possible extent in the case of a
backup.
The backup valve used in Actros also has a 2/2-way
valve which is energized when ABS is activated, in order
to prevent unintentional throughput of the rear axle
backup pressure during ABS control cycles.

Installation location (MB Actros):

frame inside, near rear axle

12 WABCO
 Description of Components EBS

Backup Valve 480 205 ... 0

Function

Central Module

Axle Modulator

Air Reservoir

WABCO 2 13
EBS Description of Components

Axle Modulator 480 103 ... 0

The axle modulator controls the brake cylinder pressures
on both sides of one or two rear axles. It contains two
independent pneumatic pressure control channels
(Channels A and B), each containing one inlet and one
exhaust valve, plus one pressure sensor, sharing one
electronic control unit. The index pressures and external
monitoring functions are provided by the central module.

In addition, two speed sensors monitor and evaluate the

wheel speeds. In the event of a tendency to lock or to
spin being detected, the index value provided is
adjusted.

Two sensors can be connected for monitoring lining

wear.

The axle modulator has one additional port for

connecting a backup pneumatic braking circuit. One
double check valve per side transmits the higher of the
two pressures (electro-pneumatic or redundant) to the
brake cylinder.

Installation location (MB Actros):

rear axle

14 WABCO
 Description of Components EBS

Axle Modulator 480 103 ... 0

Function

Central Module

Air Reservoir Air Reservoir

Tristop® Tristop®
Brake Brake
Actuator Actuator

Backup Valve

WABCO 2 15
EBS Description of Components

Trailer Control Valve 480 204 ... 0

In the Electronically controlled Braking System, the trailer
control valve is used as a control element to output the
hose coupling pressures.

The trailer control valve consists of a proportional

solenoid valve, a relay valve, a breakaway emergency
valve and a pressure sensor. Electrical actuation and
monitoring are effected by the central module.

The control current determined by the electronics is

converted by the proportional solenoid valve into control
pressure for the relay valve. The output pressure of the
trailer control valve is proportional to that pressure.

The pneumatic actuation of the relay valve is effected by

means of the backup pressure from the brake signal
transmitter and the output pressure from the hand brake
valve.

Installation location (MB Actros):

near air reservoirs

16 WABCO
 Description of Components EBS

Trailer Control Valve 480 204 ... 0

Function

Central Module

Brake
Signal
Transmitter
Air
Reservoir

Front Axle

Hand Brake Valve

Other Components
Other components of the electronically controlled braking Proportional Relay Valve:
system: 480 202 005 0 (8x4 vehicles)
480 202 004 0 (all other vehicles from 08/97)
n ABS solenoid valves
n wheel speed sensors
Backup Valve:
480 205 001 0
n brake lining wear sensors
n ASR solenoid valve for 6x2 and 6x2/4 vehicles which
Axle Modulator:
480 103 002 0 (4x2 vehicles up to 07/97)
pneumatically disconnects the additional axle from
480 103 001 0 (6x2, 6x4, 6x2/4 and 8x4 vehicles up
the driving axle during ASR control cycles.
to 07/97)
480 103 004 0 (4x2 vehicles from 08/97)
Part Numbers 480 103 005 0 (6x2, 6x4, 6x2/4 and 8x4 vehicles from
(for the components in Actros):
08/97)
Central Module:
Trailor Control Valve:
446 130 000 0 (all vehicle types up to 07/97)
480 204 001 0
446 130 005 0 (4x2 semitrailer tractors from 08/97)
446 130 004 0 (all other vehicles from 08/97)
ABS Solenoid Valve:
472 195 008 0
Brake Signal Transmitter:
480 001 000 0

WABCO 2 17
EBS Description of a 4S/4M System

Function of Electro-Pneumatic Signal processing and error monitoring for the rear axle
are covered by the axle modulator, permitting the sensor
Portion of the System values to be made available to the central module via the
data bus.
The electro-pneumatic portion of the tractor system and
its signal path operate via Operation of Pneumatic Backup
n Brake signal transmitter The front and rear axle circuits follow different backup
Two distance sensors establish the index value procedures: The front axle circuits uses the additional
which is transmitted after modulation of pulse backup principle whilst the rear axle circuit is equipped
width; two switches are used to confirm the index with a backup which can be actuated via a solenoid
value. valve.
n Central module
To establish the index value for the individual Additional Backup on the Front Axle
axles, and system control
The pneumatically operating front axle backup circuit
n Proportional relay valve uses a
to control the pressure for the front axle
n ABS solenoid valves n Brake Signal Transmitter
for rapid ABS pressure control cycles at the wheel with 2 pneumatic circuits (front and rear axles),
brakes on both sides of the front axle and a
n Backup valve n Proportional Relay Valve
for retaining the backup pressure of the rear axle relay valve with combined pilot control via the
n Axle modulator pneumatic front axle circuit and the proportional
with integrated control unit to control the brake solenoid valve
pressure on both sides of the rear axle(s). to act on the brake cylinders of the front axle.
EBS can be switched on either via the electrical driving
switch (Cl. 15) or by actuating the brake signal When the brake signal transmitter is actuated, there is
transmitter and its integrated brake switch. output of electro-pneumatic pressure via the proportional
valve. As a ratio of the actuating force, the proportional
The brake pedal’s travel measured is interpreted as the valve is supplied with pressure from the brake signal
index retardation and converted by the central module, transmitter, with a delay in pneumatic backup pressure.
taking into account a number of criteria, into the index
pressures for the front and rear axles. This pressure is added to the electro-pneumatic output
pressure. The output pressure from the proportional
The index value for the axle modulator is transmitted by valve is adjusted to the given index pressure by adjusting
the central module via a system bus. The axle the electro-pneumatic pressure accordingly.
modululator reads and controls the brake pressures of
the wheel brakes on both sides of the rear axle. The In the event of the electro-pneumatic system failing, the
brake pressure of the front axle is controlled by the pneumatic backup pressure is allowed to pass through.
central module via the proportional relay valve with the
integrated pressure sensor. Because of the necessity of holding back the redundant
brake pressure of the front axle versus the electro-
The wheel speeds are read by the sensors known from pneumatic output pressure (e. g. for optimizing wear or
the ABS system and are used, among other things, as integrating a sustained-action brake), the “electrical
the input value for the pressure control and regulating brake signal transmitter“ has predominance over the
algorithms, and for the ABS and ASR functions. pneumatic output pressure of the front axle at the brake
signal transmitter (2nd pneumatic circuit of the brake
In order to achieve lining wear control, the lining wear, signal transmitter).
sensors read the degree of wear of the linings in the
individual wheel brakes. The sensor signals from the
front axle are picked up by the central module, those
from the rear axle by the axle modulator.

18 WABCO
 Description of a 4S/4M System EBS

Rear Axle Backup

The pneumatic backup on the rear axle uses a

n Brake Signal Transmitter

with 2 pneumatic circuits (front and rear axles), a
n Backup Valve
with a 2/2-way solenoid valve, a 3/2-way valve and
a relay valve, and
n Double Check Valves
integrated in the axle modulator for the rear axle
to act on the brake cylinders on the rear axle.

With properly operating EBS, i. e. electronic pressure

output is possible on the rear axle, the 3/2-way valve is
brought into the “suppress backup“ position by the
electronical output pressure on the left rear wheel.

Operation of Trailer Control

Trailer control is effected via a dual-circuit electro-

pneumatic trailer control valve (one circuit being electro-
pneumatic, the other purely pneumatic). This is actuated
by the central module. A proportional valve and a
pressure sensor allow electro-pneumatic control of the
trailer’s actuating pressure.

The function of the purely pneumatic part of the trailer

control valve is similar to that of a conventional trailer
control valve (actuation from port 42 via circuit 1,
breakaway safeguard, pressure control through parking
braking system).

The pneumatic control port is fed by the brake signal

transmitter’s backup port for the rear axle and will not
allow any pressure to pass until the ratio falls to below
pel/p42 ~ 0.5. If that ratio is exceeded, the electro-
pneumatically actuated pressure acts on its own.

WABCO 19
EBS Description of a 4S/4M System

Electrical/Electronic Circuits

The electronically controlled braking system is by means of an electronic switch in the event of a fault.
electrically energized via two non-fused feed lines. The connection between the central module and the axle
Terminal 30a: modulator is effected via a separately specified CAN
Voltage supply for brake signal transmitter 1st circuit, system bus.
proportional relay valve, trailer control valve and the ABS For actuating, and exchanging data with, electrical
valves. braking systems in trailers, the central module has an
Terminal 30b: electrical data interface to ISO 11992.
Voltage supply for brake signal transmitter 2nd circuit, The trailer system does not receive its energy supply
axle modulator and backup valve. from the central module.
The data stored to Part 2 of ISO 11992 are processed by
For communicating with other vehicle systems (engine, the central module according to their relative importance
transmission, retarder), the central module has a bus and their function, and exchanged for communication
interface. with other bus users depending on the vehicle
The axle modulator, the ABS valves, the porportional manufacturer’s bus specifications.
relay valve for the front axle and the trailer control valve The brake signal transmitter contains two separate
can be separately switched off via a short-circuit proof electrical circuits. Via two switches, the actuation
electronic switch integrated in the central module. process is recognized. These switches perform the
The external pressure and wear sensors are earthed in following functions:
the central module and the axle modulator. Connection
to vehicle earth is not permissible. The sensors of the n perceiving the commencement of the braking
central module are earthed in a neutral point in the process,
vicinity of the central module (l <= 1 m). Another neutral
point (l <= 1 m) is used as a connecting point for energy
n activating the EBS (when driving switch is in the
“off“ position),
earth (backup valve, brake signal transmitter, axle
modulator). The earthing wires of the ABS valves lead n if not activated, the offset values of the index value
back to the central module where they can be separated sensors are calibrated, and monitored.

20 WABCO
 Description of a 4S/4M System EBS

The non-contact distance sensors supply the central Brake Force Distribution
module with the electrical index braking value in the form The distribution of the brake forces across the front and
of signals with modulated pulse widths. Both signals from rear axles is dependent, among other factors, on the
the electrical backup transmitter are evaluated equally. comparison of the actual and index values for vehicle
retardation within the program for the process of
The brake pressures on the front axle and at the “control“ "retardation control". The controlling variables are the
hose coupling are controlled by means of proportional wheel speeds picked up by the speed sensors. The
relay valves with regulated current. The actual pressure evaluation of the readings from the wheel speed sensors
sensors are integrated in valve modules. The actual show the differences in the slip of the front and rear
values are transmitted in the form of analog signals. axles, i. e. differential slip control. With the best possible
brake force distribution, there is ideally no differential slip
Reading the axle load is no longer necessary. The between the axles of the towing vehicle. The pressure on
differential slip which changes with the vehicle’s load is the front and rear axles is controlled in such a way that
picked up by the wheel speed sensors and evaluated by the differential slip approximates zero.
the central module which also actuates the valves.
Brake Lining Wear Control
The central module can display the system status via a In a non-critical braking process the brake force
yellow EBS info lamp and a red warning lamp. An distribution is adjusted according to the wear signals
additional yellow info lamp indicates that ASR is in received, i.e. a perceived variance in lining wear. The
operation. The functions and colours of the lamps may, pressure on the wheel brakes showing more wear is
however vary with different vehicle manufacturers. reduced slightly, the pressure on the wheel brakes
Mercedes-Benz, for instance, use a display on the showing less wear being increased correspondingly,
dashboard showing the status of the system. thus ensuring that the total retardation requested by the
driver does not change.
For monitoring brake lining wear, potentiometers (or, as
an alternative in the case of drum brakes, limit switches) Trailer Control
must be provided for input to the central module from the Trailer control is achieved both electrically via the motor
front axle. The rear axle lining wear sensors provide input vehicle interface (ISO 11992) and pneumatically via the
to the axle modulator; the readings are transmitted to the electro-pneumatic trailer control valve. For reasons of
central module via the control system bus. For the economy, no sensors are being provided for coupling
individual axles, the sensors are separately supplied with forces. The deceleration of the motor vehicle initially lies
short-circuit proof voltage of 5 volts. around the middle of the EC braking band. If the
deceleration of the trailer also lies in the middle of the
Control Functions band, no coupling forces occur. If the trailer deviates
from the middle band position, the motor vehicle’s ECU
Retardation Control will perceive this by means of the retardation control
Retardation control is used to adjust the level of brake portion of the program, and will adjust the trailer’s
pressure to the retardation as desired by the driver actuating pressure accordingly.
(defined as z in %). Any higher response threshold of the trailer’s brakes will
At equal pedal actuation, the vehicle is always retarded be compensated by a corresponding inshot. That inshot
at the same rate, regardless of the load carried at the of pressure in the trailer’s control line (yellow) will be
time. approx. 2 bar when the braking process is commenced.
To make the driver subjectively perceive any Most problems known today are solved with this
deterioration caused by a change of the coefficient of approach.
friction on a wheel brake (e.g. fading when going WABCO has been instrumental in standardizing the
downhill), retardation control will end any adaptation electrical motor vehicle/trailer interface (ISO 11992).
process as soon as a given (fixed) maximum value has
been reached.

Also included in retardation control are an adaptation to

the brake hysteresis. Every time the brake is released,
the releasing steps are selected in such a way that the
brake force is adjusted immediately. This function
achieves the earliest possible release of the brake, i.e. a
sensation similar to driving a passenger car.

WABCO 21
EBS Description of a 4S/4M System

EBS integrates the following time-tested functions: Supporting Functions

Anti-Lock Function (ABS) Generating The Nominal Brake Value
The control logic is aware, from the speed behaviour of (Index Value)
the wheels, whether one or several wheels are showing The brake pedal travel picked up by the sensors in the
a "tendency to lock" and will then decide whether the brake signal transmitter is transmitted to, and
respective brake pressure is to be lowered, maintained "processed" by, the central module. For this purpose, the
or increased. The wheels of the rear axle are controlled travel is converted into nominal retardation as shown by
in analogy to this concept within their optimal range the characteristic curve as illustrated below.
(individual control Ø IR).
On vehicles with 3 or 4 axles which use 4S/4M systems,
the non-sensed wheels are also laterally controlled.

On roads with extreme differences in the nearside and

offisde coefficients of friction, vehicles are very difficult to
control, if at all, when ABS operates, due to the
differences in brake pressure buildup (yawing incidence).
For this reason the brake pressure on the front axle
wheel brakes is not controlled independently, permitting
the driver to take steering action (modified individual
control Ø MIR).

If there is a tendency of the driving wheels to lock on a

low friction surface while the sustained-action brake is
being used, thereby causing the vehicle to be potentially
unstable, the vehicle’s CAN bus will switch off the ABS Determination of nominal brake value
and the sustained-action brake, thus ensuring that
stability is maintained. Pressure Control on Front And Rear Axles And
Electro-Pneumatic Trailer Actuation
Drive Slip Control (ASR) The index pressures computed from the nominal brake
Similar to the ABS function, the control electronics will value using the overriding control algorithms are output
perceive whether the driving wheels are within the stable in the pressure control curcuits for the front and rear
range of the µ-slip curve as the vehicle is being axles, and for trailer control. To improve the pressure
accelerated. control properties, the magnetic flux is controlled within
the solenoid valves.
If the wheels show a "tendency to spin", the CAN bus and
the engine control system will adjust the engine's Speed Sensors And Tyre Coordination
performance and/or brake the wheels of the driving axle Reading the wheel speeds is similar to the procedure
via the axle modulator. Activated ASR control is known from the ABS system. Automatic tyre coordination
displayed via a control lamp. compensates for any difference in nominal tyre sizes and
thus the rolling circumferences among axles. If
impermissible pairs of tyres are used, this will be
recognized as a defect.
If tyre sizes are changed, this requires resetting of the
parameters.

22 WABCO
 Error Detection EBS

Error detection measures are used to avoid the effects of pneumatic redundant pressures are monitored.
system failures and/or to alert the driver to any functional
defects. In part the error detection principles are similar Front axle brake pressure insufficient / trailer control
to those of a conventional ABS (monitoring of ABS valve brake pressure insufficient
valves, speed sensors, computer hardware). Checks are made to establish whether there is a
minimum brake pressure (at the front axle or at the trailer
A large part of the monitoring activities, however, relates control valve) at a certain magnetic energy.
to specific operational areas of the EBS (EBS sensor
systems, EBS solenoid actuation, brake pressure output, Excessive rear axle pressure deviation (nearside-
data transmission via CAN bus). offside)
During normal braking operation (neither ABS nor ASR
In addition to the speed sensor signals, EBS evaluates controlled) the brake pressure readings have to be close
numerous other sensor singals, checking them for to identical on both sides of the rear axle. If the brake
accuracy. pressure exceeds a certain tolerance range, the system
will identify an error.
Nominal Value Sensor Systems (Sensors And
Switches) Failure of rear axle redundancy
The brake signal transmitter supplies two sensor signals In certain situations (stationary vehicle, parking brake on)
and two switch signals. The sensor signals (modulated the electrical brake pressure output on the front and rear
for pulse width) are checked for adherence to the axles will be prevented. If the driver now depresses the
permissible range and for mutual deviations. The switch brake pedal, the front and rear axles will be braked by
signals (digital) are checked for their proper switching means of pneumatic redundancy. If the front axle brake
status. pressure exceeds a certain value, a certain minimum
pressure also has to be present at the rear axle. If this is
Brake Pressure Sensors (Front and Rear Axles, not the case, the system will identify an error.
Trailer Control Valve)
The signals (analog) of the pressure sensors in the Rear axle redundancy cannot be switched off
pressure control circuits are checked for adherence to The output of pneumatic redundancy pressure at the rear
the permissible range. axle is usually prevented by the redundancy valve. If, due
Please note: The wiring of both rear axle pressure to an error, this can no longer be prevented, it may no
sensors is not externally accessible - this is part of the longer be possible to reduce the rear axle brake pressure
internal wiring of the axle modulator. when ABS control takes place (because the rear axle
redundancy pressure which is not subject to ABS will
Wear Sensors (Front and Rear Axles) reach the brake cylinders on the rear axle). In this
The signals (analog) of the wear sensors are checked for situation, an error will be recognized.
adherence to the permissible range.
EBS monitors the transmission of data
EBS monitors the actuation of the dedicated EBS
solenoid valves. n between the EBS central module and the axle
modulator (system bus)
Front Axle Proportional Relay Valve / Trailer Control
Valve
n between the EBS and other system control
equipment (vehicle bus)
The continuous magnets (pressure proportional to the
magnetic flux) of the front axle proportional relay valve n between the towing vehicle and its electronically
and the trailer control valve are monitored for their proper braked trailer.
actuation status.
If no communication is possible, or if communication is
suddenly terminated, an error will be recognized.
Inlet and Outlet Solenoid Valves for Rear Axle
Modulator
The inlet and outlet solenoid valves of the rear axle are
located within the axle modulator. The magnet wiring is
not accessible.

EBS monitors the brake pressure output. Both the

electrically controlled brake pressures and the

WABCO 2 23
EBS EBS „Emergency Operations“

Once an error has been detected, certain functional Pressure control operation / Auxiliary pressure
sectors of the EBS will usually be deactivated. Functions control
which are not impaired by the failure will be maintained. Control of the brake pressure will usually require the
For the operation of EBS with limited functional scope, signal from the brake pressure sensor. If this signal is no
the term „emergency operations“ is commonly used. longer available, it is possible to generate brake pressure
electrically by using certain auxiliary quantities. This we
The following functions can be deactivated in the event call pressure control operation or auxiliary pressure
of a defect: control. The accuracy of the pressure generated is,
however, limited compared with proper pressure control.
Operation without ABS function (Possible causes: failure of a pressure sensor signal, ...)
The ABS function can be deactivated at one individual
wheel, at one axle, or for the whole vehicle. (Possible Redundancy operation
causes: defective speed sensor signal, ABS valve If electrical pressure output is no longer possible, the
failure, ...) axle in question is braked by means of the pneumatic
redundancy pressure. (Possible causes: defective
Operation without ASR function solenoid or defective solenoid wiring, ...)
Drive-slip control can be deactivated either partially or
completely. If it is shut down completely this means that
both brake control and engine control will be shut down.
Partial deactivation means that only brake control has
been shut down. (Possible causes: defective speed
sensor signal, ...)

24 WABCO
 Testing the EBS EBS

When testing the EBS, the following special

features must be taken into account:

n Testing the Backup Valve: n Testing on the Roller Dynamometer:

When the vehicle is stationary, with the parking For testing a vehicle with an electronic braking
brake on and the brake pedal depressed, the axle system (MB Actros) on a roller dynamometer, the
modulator is switched off; this allows the backup following criteria must be met:
valve on the rear axle to be checked using a The wheels on one axle are inert, the others are
pressure gauge which is connected to the rear turning at a speed < 12 k.p.h. for at least 20
axle brake cylinder. Now the failure of the seconds,
electronic circuit is simulated. In this case the or
output pressure must be approximately half the the vehicle is stationary, the parking brake is
supply pressure. released, the brake pedal is actuated for more
n Maximum Pressure Output:
than 5 seconds after the ignition has been
switched on.
When the brakes are actuated > 80%, the
Now the maximum EBS brake pressures can be
pressure output must be at its maximum on the
measured. The system is in working order.
front and rear axles, and at the control hose
coupling (yellow).
n Pressure Inshot:
By tapping the brake pedal (brake lamp switch
closed), the pressure inshot, brief pressure pulse
of approx. 2 bar, can be checked at the control
hose coupling (yellow) using a pressure gauge. At
the same time, the readings for the contact
pressures of the brakes on the motor vehicle can
be taken.

WABCO 2 25
EBS Operation and Dials

Dashboard (Type MB Actros)

Position 1: display, red section SYSTEM Button

Position 2: display, green section This button can be used to display information on the
Position 3: operating keys for vehicle diagnostics outside temperature, operational, service or diagnostic
data:
pushed once = operational information
pushed twice = service mode
pushed three times = diagnostic mode for the first
electronics system
pushed repeatedly = diagnosis mode for additional
electronic systems.

QUIT Button
This button can be used to
n suppress the display of category “0“ defects
n suppress the display of information in the green
section
n end the diagnostic mode.
RESET + QUIT Buttons
These buttons can be used to
n delete any defects stored from the error memory
The display consists of a green and a red section. (by authorized workshop staff)
The green section shows operational and control n and for executing other non-EBS functions which
information, and the outside temperature. The red are not covered by this document.
display section is used for displaying warnings and
defects. Any defect in an electronic system appears in INFO Button
the red section of the display in the form of an error code, This button is used to request additional information in
which is then stored and allocated to a group of defects. the electronics system selected, such as additional data
At the same time, the warning buzzer comes on. of an operational, service or diagnostic nature, and the
location of a defect.

26 WABCO
 Error Code Description EBS

Mercedes-Benz Type Actros The errors can be deleted only while the vehicle is
stationary.
The display of the status of the system and the warning For testing, the following are required:
facility for the driver in the event of a defect are achieved
via the CAN bus and the display matrix shown below. n full supply pressure
The diagnostic requirement for as disparate a recognition n 24 volts operating voltage.
of all errors as possible for easy location of defects by the
service department has been taken into account in the
safety concept.
If the system detects a defect, this is stored in the central
module. This also applies to any errors found in the axle
modulators. The central module stores up to 16 system
errors for the purpose of diagnosis.

1st example: 1 10 02

1 = defect of intermediate importance

10 = control unit
02 = undervoltage

ON-BOARD Diagnosis:
If the red display, for instance, shows the system
abbreviation ‘EPB’ with an error code (see top right-hand
side of this page), the electro-pneumatic braking system
is defective. The first digit beneath the letters ‘EPB’
indicates the significance of the defect. Actros provides
for significance ratings 0, 1 and 2.
0: slight defect = display may be suppressed The photograph shows the red display returning a
(using QUIT key) currently existing defect.
1: intermediate defect = cannot be suppressed
2: serious defect = cannot be suppressed. 2nd example: 1 22 03
The two digits following indicate the error path, and the
last two digits provide information on the type of error or 1 = defect of intermediate importance
defect. In the event of several errors or defects existing 10 = redundancy valve
at any one time, only the defect with the greatest 02 = disconnected feed line
significance will be displayed, and its significance may, in
individual cases, increase from 1 to 2. If this happens and OFF-BOARD Diagnosis:
an error is displayed with a first digit of ‘2’ which is not The display instrument is also used for OFF-BOARD
listed in the error code table below, this may be found diagnosis as an intermediary between the control units
under the first digit of ‘1’. and external testing equipment such as the Diagnostic
Any error appearing in the green (2) display only Controller, or PC diagnosis. After connection setup, the
currently exists if it is preceded by the letter ‘a’. Any red display (1) only shows the first digit, i. e. the error
errors perceived will be stored in the corresponding error significance. When OFF-BOARD diagnosis is used, the
memory of the ECU. SYSTEM, INFO and RESET buttons are deactivated.

WABCO 2 27
EBS Diagnosis

Diagnostic Controller Ill. 2: Connection of the Diagnostic Controller

The Diagnostic Controller is a computer which is able to

exchange data with control units (which are computers,
too). In this context, data shall mean the following:
n error messages stored in the ECU
n commands transmitted from the Controller to the
ECU where they trigger certain procedures.

In order to be able to communicate with an ECU, a

special program is required. This program is stored on
the respective program card. Program card and ECU
must be based on the same system!

The Diagnostic Controller Set (446 300 331 0) comprises

the following:
n Diagnostic Controller 446 300 320 0
n Carrying Case 446 300 022 2

Accessories:
PIN Assignment:
n Program Card 446 300 7xx 0
n Connecting Cable (ACTROS) 884 904 933 0 Plug Socket
n Multimeter Cable, black 894 604 301 2 PIN 2 +24 volts (red) PIN 1
n Multimeter Cable, red 894 604 302 2 PIN 1 ground (brown) PIN 2
n Keyboard 446 300 328 0 PIN 4 K-line (yellow) PIN 8

The following ECUs can be tested:

n 446 130 000 0
n 446 130 004 0 Ill. 3: Diagnostic Socket
n 446 130 005 0

In addition, it is possible that other ECUs can be tested

using this program card.

Connecting the Diagnostic Controller to the

Vehicle’s Diagnostic Socket:
One end of the connecting cable is plugged into the
Diagnostic Controller (Ill. 2), the other to the diagnostic
socket in the control box (Ill. 1) of Actros.
Ill. 1: Diagnostic Socket

28 WABCO
 Diagnosis EBS

Program Description
1 Diagnosis
1 Error Location
2 Actuation
1 ASR on/off
2 Pressure Output
1 Prop. valve FA
2 Axle modulator RA
3 Axle modulator AA
4 Trailer control valve*
3 Pulse/Test Program
1 Modulator FA left
2 Modulator FA right
3 Axle modulator RA*
4 Axle modulator AA*
5 ASR deactivate AA*
4 Backup System
1 RA backup program
2 FA backup characteristic raise
3 Trailer control valve backup program
5 ABS deactivate trailer*
3 Testing and Measuring Values
1 Speed Sensors
1 Sensor FA left
2 Sensor FA right
3 Sensor RA left
4 Sensor RA right
5 Sensor AA left*
6 Sensor AA right*
2 Pressure Sensors
1 Pressure sensor FA
2 Pressure sensor RA
3 Pressure sensor AA*
4 Pressure sensor trailer control valve*
3 Wear Sensors
4 Brake Signal Transmitter
5 Switch Positions
1 Brake switch
2 Button ASR off-road
3 Button ABS off-road*
6 Voltages
4 Control Unit Data
1 Parameters
1 display / change**
2 transmit
1 ECU - DC
2 DC - ECU
2 WABCO data
2 Commissioning*
3 Multimeter * only if installed on the vehicle
1 Direct voltage ** available only after entering PIN
2 Alternating voltage FA = Front Axle
3 Resistance
RA = Rear Axle
4 Options AA = Additional Axle
1 Help texts
2 Variant
3 ECUs for testing
5 Special Functions

WABCO 2 29
EBS Diagnosis

Using the Diagnostic Controller any major leakages within the pneumatic system
will be detected.
Description of the Menu Items for Please note: To make sure that the vehicle cannot
“jump“ from the roller when tested on the
Program Card 446 300 7xx 0
dynamometer, the rear axle is always braked as
the front axle is being tested, and when the rear
1. Diagnosis
axle / additional axle is tested, the front axle is
1.1 Error Location braked as well.
First the error memory of the ECU is read out, and In all test / pulse programs, a maximum braking
the errors are sorted as they appear in the display. pressure of 2 bar is output on the axles included.
The user then has the option of either repairing the If the PIN code has been entered, a braking
defect or have the next error displayed. Once all pressure can be freely selected between 1 and 10
errors have been displayed, the error memory can bar.
be cleared. During the deletion process, diagnosis
is suspended briefly (to give the ECU the 1.2.3 Pulse / Test Program
opportunity to once again detect any errors or Special pulse or test programs can be used to
defects, and store them in the error memory). make sure that the wiring and pipes are in order,
This is followed by the error memory being read in and that the front axle’s ABS valves, the axle
once more, and the findings shown. modulators for the rear axle and the additional
axle, and the ABS cut-off relay for the additional
1.2 Actuation axle are working properly.
“Actuation“ is used to actuate certain components Here, too, the axle which is not being tested is
within the EBS system to check whether they are braked to prevent the vehicle “jumping“ from the
in proper working order. For this purpose, various roller dynamometer when the brake force is
test programs are executed for individual excessive.
functional groups. Since these programs usually
have to be run while the vehicle is on the roller 1.2.4 Backup System
dynamometer, the ASR function is deactivated In the event of the control unit failing altogether, it
when tests for the rear axle / additional axle with must be possible to use the backup system for
sensors are selected in order to prevent that axle pneumatic braking of the vehicle. For checking
being braked. Only modules are offered for whether that this system is in good working order,
selection for which the parameters of the control three test programs are available which check
unit show that they have been installed on the different parts of the system. It is advisable to
vehicle. For details on test procedures, please check the backup system everytime the vehicle
refer to the instructions for using the program card. has been serviced or repaired!

1.2.1 ASR On/Off 1.2.5 Deactivation Trailer ABS

Manually switching the ASR function on/off. In The ABS deactivation relay for the trailer is
addition, the current status of the ASR (on/off) switched on and off once a second for ten
appears on the display. seconds. To check that it is working properly, a
corresponding test plug with a lamp must be
1.2.1 Pressure Output plugged into the trailer socket, or a voltmeter
The various steered axles (FA, RA, AA, trailer connected.
control valve) a pressure of 2 bar can be output
individually (if PIN has been entered, this is freely 1.3 Testing and Measuring Values
selectable). When the test program has been This part of the program can be used to display
initiated, the pressure picked up by the various switch positions and measuring values. If a sensor
pressure sensors before and after output are is not available, or if it supplies an invalid signal,
displayed. The first reading (“pressure reading 1“) the program will not show the (wrong) measuring
should be 0 bar since this reading is taken at value but a number of dashes “----“ instead. This
atmospheric pressur. The second reading always indicates a defective or inactive sensor.
(“pressure reading 2“) should be approx. 2 bar or This will happen only for sensors which, according
the preselected braking pressure (after entering to the parameters set, have been installed on the
the PIN). vehicle.
With these programs it is possible to verify that the
various control valves, together with the pressure
sensors, are in proper working order. In addition,

30 WABCO
 Diagnosis EBS

1.3.1 Speed Sensors component number from the control unit (menu
The output voltage amplitudes of the speed item: “read WABCO data“).
sensors are displayed, together with the In addition it is possible to display the parameters
measured wheel speeds. In order to be able to which apply to the vehicle. After entering the PIN
detect any wobble of the pole wheel, both the code, which is restricted to authorized workshop
current and the minimum / maximum amplitudes staff, the “special functions“ menu item can be
are shown. The display will appear at wheel used to change the parameters and rewrite them
speeds > 1.8 k.p.h. Since the wheel speed into the control unit. Furthermore, the data can be
sensors are usually tested on the roller transferred from one control unit to another using
dynamometer, the ASR function is switched off the Diagnostic Controller (this also requires entry
when the values for the rear axle’s / additional of the PIN code).
axle’s sensors are selected in order to prevent If the connected control unit contains a set of
braking. parameters unknown to the program, the
parameter designations or their contents are not
1.3.2 Pressure Sensors
displayed in plain text. In this case, please refer to
The readings for the braking pressure on the
the documents on the control unit for the
steered axle, (front axle, rear axle, additional axle,
corresponding text.
trailer control valve) can be displayed individually.
After the last of the parameters has been reached,
Both the index pressures and the actual pressure
or after “END“, the program will inquire whether
readings are shown.
the changed values are to be stored in the ECU. If
1.3.1 Wear Sensors this is confirmed, the program will, after a safety
The brake lining wear is shown [%] for all axles inquiry, request entry of the date. This will be
with sensors. stored in the control unit, together with the
parameters.
1.3.4 Brake Signal Transmitter
In addition to the output signals [ms] of the two 2. Commissioning
circuits of the brake signal transmitter, the braking By means of “Commissioning“, the whole of the
performance [%] and the index retardation [%] are ABS can be tested, and a test log printed (e. g.
also displayed. after initial installation or comprehensive repairs).
Commissioning is divided into two parts:
1.3.5 Switch Positions
The status of the following switches can be n functional testing
displayed: n printed log
n brake switches 1 + 2 (in the brake signal Please note:
transmitter)
n button ASR off-road If functional testing has been commenced, this has
n button ABS off-road to be processed step by step. It is not possible to
go back to a previous step, or to skip any steps.
The program cannot perceive which buttons have
actually been fitted in the vehicle. For this If the Diagnostic Controller’s voltage supply fails,
reason, it will always display all buttons which can all data previously measured and stored for the
be connected to the ECU. printed log are deleted. This is why it is important
that the diagnostic connection is never severed if
1.3.6 Voltages
a printed log is required.
The following supply voltages are displayed:
n Terminal 15 (Pin X1/7) The data for the printed log are stored in the
n Terminal 30a (Pin X1/8) Controller the moment its user confirms a
n Terminal 30b (Pin X1/9). measuring process or an inquiry by pushing a
In addition to the voltage readings, their index button.
voltages are shown. If the actual voltage at In some cases the program may decide
Terminal 30b lies above its minimum index automatically whether any step within the testing
voltage, the cause is often a defect in the axle procedure has been properly carried out (e. g.
modulator circuit. For this reason, “check AM“ will pushing a button, pressure readings). If this does
be displayed. not occur, the user is given a yes/no option (e. g.
after pulse programs).
1.4 Control Unit Data
This menu item can be used to read out and
display the manufacturing data and the

WABCO 31
EBS Diagnosis

If an error has occurred during a testing 3. Multimeter

procedure, this can be executed once again. In The integrated multimeter function can be used to
addition, it allows the commissioning process to be take electrical readings on the vehicle. Only the
aborted prematurely. A test log can, however, still desired measuring function (direct voltage,
be printed. alternating voltage or resistance) needs to be
selected. The measuring range is set
2.1 Functional Testing
automatically by the unit.
For functional testing, the vehicle must be
stationary (wheel speed must be zero on at least Application:
one axle), and no errors may have been stored. direct voltage: on-board voltage
The vehicle may be moved only if the program alternating voltage: sensor voltage
expressly requests this. For the program’s exact resistances: valve, relays, sensors,
execution sequence, please refer to the operating line continuity
instructions for the program card.
PLEASE NOTE:
2.2 Printing the Test Log The multimeter is designed only for voltages within
After the test, a test log can be printed. the vehicle’s range (low potential).
As mentioned previously, the Controller must stay
4. Options
connected to its voltage supply. Any disconnection
at any time will delete all data. 4.1 Help Texts
With this function, the user can obtain additional
The connection to the printer is established by
operating instructions. When this function has
means of the rear 25-pole socket and a serial
been switched on, more detailed information on
printer cable. The cable must have DB 25 plugs
the program will appear at the appropriate times
(not sockets!) on both ends.
between the various steps.
4.2 Version
This function shows the status of the components
supplied (Controller and program card).
4.3 ECUs for Testing
Output of WABCO numbers for the control units
which are supported by the program. At present
this applies to the following control units:
n 446 130 000 0
n 446 130 004 0
n 446 130 005 0
5. Special Functions
After entering a Personal Identification Number
(PIN code), menu item 1.4 (parameters) can be
cleared. The PIN may be issued only to
specialized staff specifically authorized by the
vehicle manufacturer.
The program works with printers which are
EPSON FX compatible, with a serial interface
(RS232). The printer’s transmission parameters
must be set to the following configuration:
speed: 1200 baud
data bits: 8
stop bit: 1
parity bit: X ON / X OFF

32 WABCO
 Diagnosis EBS

Using a PC Ill. 2: Connection of Laptop with Diagnostic Connection in

Actros
As an alternative to the Diagnostic Controller, a PC can
be used for vehicle diagnosis.

Hardware Requirements
n notebook / laptop wherever possible
n recommended PC 486 or higher
n 4 MB main memory, colour display 640 x 480
n approx. 3 MB available harddisk space, plus
3½" floppy disk drive
n 1 COM interface (9-pin connection) for WABCO
Diagnostic Interface 446 301 021 0
n Windows 3.xx, Windows 95

Ill. 1: Hardware Components

In preparation for tests on the vehicle, this Diagnostic When the connection has been established as shown
Interface (No. 446 301 021 0) must be connected to the above, testing may commence. Now all functions
PC and the vehicle’s diagnostic socket (Ill. 2). When the described under “Diagnosis using the Diagnostic
ignition is switched on, this provides the power supply for Controller“ can be done via PC diagnosis.
the Diagnostic Interface (lamp in the interface is on).

Components
Program (diskettes) 446 301 5xx 0
Diagnostic Interface Set 446 301 021 0
(consisting of Interface and connecting cable for the PC)
Connecting Cable (ACTROS) 884 904 933 0

WABCO 2 33
EBS System Design

EBS- Brake System for Track 4 x 2

Legende 3. Proportional Relay Valve 5. Axle Modulator

1. Central Module 4. Solenoid Modulator Valve - ABS 6. Backup Valve
2. Brake Signal Transmitter 7. Trailer Control Valve

34 WABCO
 Function Scheme EBS

Legende

1. Brake Signal Transmitter (BWG)

2. Proportional Relay Valve
3. Solenoid Modulator Valve - ABS
4. Speed Sensor
5. Wear Sensor
6. Backup Valve
7. Axle Modulator
8. Trailer Control Valve

Load Empty Valve in Brake Signal Transmitter

with gearing
i = 1 : 1 bei p4 = p 21 (Failure Axle Modulator)
i = 2 : 1 bei p4 = p 0 bar

Proportional Relay Valve

with gearing
i=1:1

Backup Valve
with gearing, actuating only by ABS-Action at the rear-
axle and failured of Axle Modulator
i=2:1

WABCO 35
EBS

36 WABCO