Industry Technical Council
Advisory Procedure
Heavy Vehicle
Combinations
Electronic Braking
Systems
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Published by Australian Trucking Association Ltd ACN 055 583 714
25 National Circuit
FORREST ACT 2603
© Australian Trucking Association Ltd 2012
This work is copyright. Apart from any use permitted under the Copyright Act 1968 no part may be
reproduced by any process without prior written permission of the Australian Trucking Association.
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Communications Manager.
About the Technical Advisory Procedure:
This Technical Advisory Procedure is published by the Australian Trucking Association Ltd
(ATA) and Industry Technical Council (ITC) to assist the road transport industry to improve the
technical understanding of Electronic Braking Systems (EBS) and the application of EBS and
TEBS to heavy vehicle combinations.
The Advisory Procedure has been drafted to apply to a generalised range of truck/trailer and
prime mover trailer combinations. It is not, nor is it intended to be, complete or without
exceptions.
The Advisory Procedure has been developed as a guide only, for voluntary use by operators,
trailers builders and suppliers. Recommendations or procedures may not be suitable for, or
applicable to, all operators and that is a decision for each operator to make in-line with that
operator’s circumstances, practices and procedures.
Vehicle combinations must comply with the Australian Design Rules (ADRs), the Australian
Vehicle Standards Regulations, the Roadworthiness Guidelines and any specific information
and instructions provided by manufacturers in relation to vehicles, wheel systems, and other
parts.
This advisory procedure makes no endorsement of products or services. Brand names, where
used in the Advisory Procedure, are for illustrative purposes only.
Suggestions or comments about this Advisory Procedure are welcome. Please write to the
Industry Technical Council, Australian Trucking Association, Minter Ellison Building, 25
National Circuit, Forrest ACT 2603.
DISCLAIMER
The ATA makes no representation and provides no warranty that the information and
recommendations contained in this Technical Advisory Procedure are complete or without
exception. Reliance or use upon the information or recommendations is voluntary and the
user accepts all risks and responsibility for any such reliance or use. To the maximum extent
permitted by law the ATA excludes all liability to any person arising directly or indirectly out of
any such reliance or use.
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Advisory Procedure
HEAVY VEHICLE COMBINATIONS ELECTRONIC BRAKING SYSTEMS
This Technical Advisory Procedure (TAP) has been developed by the ATA-ITC (and
endorsed by the Australian Trucking Association General Council) to inform owners and
operators of the benefits and requirements of Electronic Braking Systems (EBS) on heavy
vehicle combinations. It aims to do this by identifying important parameters relevant to
braking performance, and providing reliable technical information about these systems. The
Technical Advisory Procedure places particular emphasis on good practice for achieving
improved braking stability outcomes.
Introductory note to users of this Technical Advisory Procedure:
This TAP is for guidance only - your manufacturer/supplier may have differing view in
relation to their specific product/s. This TAP is focused on encouraging you to engage and
utilize new technologies, however as some systems have differing constraints you are
encouraged to ask questions of your potential supplier about your specific application.
Introduction
The current practices in the industry and data on heavy vehicle accidents provide strong
support for encouraging increased use of EBS and TEBS (Trailer EBS). This TAP identifies
the benefits of EBS and provides guidance for operators, manufacturers, suppliers and
trailer builders.
The correct use of EBS and TEBS has been shown to increase the safety of heavy vehicle
combinations, and increased industry uptake is encouraged. The following studies
demonstrate the safety improvement provided by EBS.
National Transport Insurance (NTI) Crash Data: Major Accident Investigation Report
2009 (Page 12) – states: Inappropriate speed for the conditions continues to be the
predominant cause for heavy truck crashes in Australia. The 2007 study found that 27.4%
of reported incidents could be attributed to inappropriate speed, particularly when altering
direction. This result was comparable to prior studies with 27.3% of major incidents in
2005, and 26.1% in 2003. The vast majority of truck crashes in this segment occurred on
outbound journeys with 83.1% in the latest evaluation. This is consistent with earlier
findings of 79.6% in 2005 and 70.8% in 2003. NSW again led the result with 29.2% of
incidents, followed by Victoria with 24.7%, and Queensland with 15.7%. In 77.5% of
incidents in the 2007 research, vehicles rolled over at corners or roundabouts, and jackknives were prominent in 9.1%. Semi-trailers had 67.4% of speed related incidents, with
livestock transporters (comprising a high centre of gravity and a moving load) influencing
this result. This study of major truck accidents focuses on claims settled during 2007. This
is the third in a series of biannual quantitative evaluations tracking the behaviour of a
cohort of Australian heavy vehicle operators. This is a comparable evaluation given that the
insurer’s portfolio remains relatively constant during the course of such studies. Consistent
throughout all research is the finding that inappropriate speed for the conditions and driver
fatigue continue to be accountable for 1 in 2 heavy vehicle crashes. On a case by case
basis, to ensure consistency of the comparable model, the National Centre of Truck
Accident Research reviews all truck accidents where material damage exceeds A$50,000.
In the 2007 research the overarching finding was that there were 19.6% fewer major truck
crashes recorded, however such losses have increased by 9.2% in average cost of claim.
US-DOT (US Department of Transport) Report HS 811 099
October 2009
Crash Problem Definition and Safety Benefits Methodology for Stability Control for
Single-Unit Medium and Heavy Trucks and Large-Platform Buses(extract):
Based on 2000-2004 GES data, an average of 147,000 single-unit medium and heavy trucks
are involved in police-reported crashes per year. This study estimated that ESC and RSC
systems could have helped about 1.5 percent of those vehicles involved in crashes, which
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amounts to about 2,200 single-unit medium and heavy trucks per year. Based on 1996-2007
GES data, an average of 106,000 large-platform buses are involved in police-reported
crashes per year. This study estimated that ESC and RSC systems could have helped about
1 percent of those vehicles involved in crashes, which amounts to about 1,000 large-platform
buses per year.
ITC comment: In principle, the advantage of ESC is its function in maintaining YAW control,
which is especially applicable in road conditions where snow and ice are frequently
encountered.
Glossary
Electronic Braking System (EBS) EBS or "brake-by-wire” integrates anti-lock braking
system (ABS) technology, automatic traction control (ATC), and other key vehicle control
system features to deliver the next generation of braking control. EBS utilises electronics for
the control side of the vehicle's braking system. An electronic signal takes priority over the
air signal sent by the brake pedal to activate the brakes, improving stopping distances and
braking system performance. EBS also enables communication between towing and towed
vehicles with regard to axle loads, wheel speeds, deceleration and other variables.
All active EBS include Electronic Stability Control (ESC), although not all models of EBS
trucks have this option activated. EBS may provide a platform for future advanced safety
systems.
In a brake system with electronic brake force distribution (EBD), the amount of brake effort,
particularly on the drive axles, can be regulated according to the load imposed on each
wheel set. The aim of this is to ensure all wheels do an appropriate amount of braking for the
load carried, and no wheel set or axle group is over braked.
EBS typically combines a range of air valves used in a traditional brake system into a single
EBS modulator unit, as shown below in Illustration 1.
Illustration 1: Two examples of an EBS modulator unit
ABS Platform is a basic ABS system to which is added additional functional elements such
as ESC, ACC or Brake Assist.
CAN (Controlled Area Network) BUS is an electronic communication bus (wiring system)
for communication of information between a system of distributed micro-controllers and
sensors on trucks and trailers.
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EBS Platform is a basic EBS system to which is added additional functional elements such
as ESC, ACC and Brake Assist.
Electronic Stability Control (ESC) is a computerised technology that improves the safety
of a heavy vehicle by detecting and minimising skids. When ESC detects loss of steering
control, it automatically applies the brakes to help "steer" the vehicle where the driver
intends to go. Braking is automatically applied to an individual wheel, such as the outer front
wheel to counter, or the inner rear wheel to counter understeer. Some ESC systems also
reduce engine power until control is regained.
ESC does not improve a vehicle's cornering performance; rather, it helps minimise the loss
of control. According to the Insurance Institute for Highway Safety (US) and the National
Highway Traffic Safety Administration (US), one third of fatal accidents could have been
prevented by using ESC technology.
Note: ESC or Full Stability with Yaw Control is only a truck or prime mover system and is not
applicable to trailers.
Roll Stability Support (RSS) identifies potential roll-overs in cornering or obstacleavoidance manoeuvres and initiates automatic braking if needed. The speed of the whole
vehicle combination is automatically reduced and the danger of a roll-over is decreased. As
soon as the danger of a roll-over has passed, the RSS braking terminates. Vehicle stability
during the automatic braking procedure is maintained by continuously acting automatic loadsensing and the ABS function.
Trailer Electronically (Controlled) Brake System (TEBS) is a high-level brake control
system that communicates brake control information between sensors and actuators using
electronic CAN communication.
Managing Roll Stability
2009 NTI findings state: “Consistent throughout all research is the finding that inappropriate
speed for the conditions and driver fatigue continue to be accountable for 1 in 2 heavy
vehicle crashes”. These statistics may be reduced by industry implementing the broader
uptake and use of TEBS with Roll Stabilising Support, specifically in the semi-trailer and/or
the last trailer of a multi trailer combination. The RSS will in many cases of inappropriate
speed for conditions intervene to slow the unit before a roll occurs. This should be taken into
consideration when specifying new trailers.
Industry Position
The Industry Technical Council, a representative group of the Australian Trucking
Association, urges operators and suppliers to adopt these principles when specifying new
equipment and when assembling multi-vehicle combinations.
The benefits of TEBS have been practically demonstrated in a privately controlled
demonstration environment (in Australia) with a semi-trailer fitted with outriggers (to prevent
roll-over) and comparisons made between TEBS operating and the TEBS rendered
inoperable. The intervention capability of TEBS to manage impending roll-over was
successfully demonstrated and satisfied engineering requirements.
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FAQs
Q1:
Can I have an EBS trailer and get any benefits if I don’t have an EBS or ABS prime
mover?
A1:
Yes, provided the control unit (the EBS fitted trailer) is provided with a constant
power supply, the benefits of ABS and RSS will result. Alternatively, EBS Power Supply via
stop light circuit will provide limited ABS and Load Sensing Function (No RSS).
Q2:
I currently operate a fleet of American prime movers (12 volt) with both ABS and nonABS, what should I specify in a trailer EBS system?
A2:
The best benefits from EBS are obtained with a full 24 volt system (prime mover and
trailer/s). The higher potential of a 24 volt system allows electrical current to be carried over
a longer distance. By fitting trailers with 24 volt TEBS systems and providing a 24 volt power
supply (inverter) from non-ABS prime movers, and 24 volt signal/supply (inverted) from 12
volt ABS prime movers, a superior electrical performance outcome will result. There will also
be further benefits when using a multi-volt trailer TEBS in long combinations. For a long
vehicle, 24 volt systems have the advantage over 12 volt, provided all other variables remain
the same. These variables include the quality of connections, quality of crimping at
connectors, and the size of wires. 12 volt systems are generally limited to two trailers.
Q3:
If I have 12 volt prime movers with both ABS and non-ABS, if I provide power to the
EBS trailer are benefits of ABS and RSS available?
A3:
Yes, the ABS, RSS and load share functions will be independent provided there is
constant power supply, so those functions operate to their optimum.
Q4:
Is EBS available for multi trailer combinations?
A4:
Yes, but best results are dependent on a CAN-BUS being fitted to all trailers. A CAN
signal can be generated from the pneumatic signal for trailers towed by conventional prime
movers.
Q5:
Do I have to have disc-brakes to specify TEBS?
A5:
No: The system is independent of brake type. However, automatic slack adjusters
are recommended with drum brakes.
Q6:
What is CAN-BUS
A6:
CAN-BUS is a system of communication between two or more electronic systems.
Controller–area network (CAN or CAN-BUS) is a BUS standard designed to allow
microcontrollers and devices to communicate with each other within a vehicle without a host
computer.
Use of CAN communication enables far greater speed of signal to trailing units, and also
sharing of data between systems, allowing the truck “master” system to positively alter trailer
braking.
Key in this system is CAN communication between vehicles and trailers in a combination. By
each vehicle providing information to the prime mover, deceleration can be matched
between prime mover and trailer. Brake timing is also vastly improved. This means that the
brakes come on together, and if the unit is loaded differently over each axle group, brake
effort will be adjusted to give a far smoother deceleration, with no wheel lockup and no pull
or push at the couplings. Currently only 24 volt trucks have this full communication capability
with trailers.
The best CAN performance is achieved with a 24 volt system. 12 volt trucks currently
generating a CAN based brake demand signal to trailers can only demand brake application,
there is no two-way flow of information allowing variation of trailer braking.
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Q7:
What is the technical operation of RSS and load share functions?
A7:
For trailers equipped with Trailer EBS, advanced Roll Stability Support (RSS) logic
control units reliably prevent vehicle roll-over within its physical limits. RSS is a function
integrated in the software and hardware of the EBS modulator. The system assesses vehicle
data such as wheel speed, load information, and by means of an integrated sensor, lateral
(transverse) acceleration data. By analysing this data quickly and effectively, the vehicle
Engine Control Unit detects the chances of vehicle roll-over and automatically applies the
brakes.
Although no system can fully defy the laws of physics, and a trailer can still tip if the side
forces are extreme or increase significantly during braking, RSS does significantly reduce
this risk.
Operation is normally as follows: At a given “set point” of lateral acceleration, the Trailer EBS
(TEBS) will apply a test pressure to the brakes. This is a very low, short duration pressure
which the driver is normally unaware of. TEBS then monitors wheel speed reaction on both
sides of the axle. If both wheels react together, the acceleration is allowed to increase, all
the while applying test pressures, until the inside wheel speeds react differently from the
outside. This means the wheels on the inside of the curve are either off the ground, or very
close to it. At this point, TEBS applies braking to slow the combination road speed.
Q8:
Does TEBS have a weight scale function?
A8:
Yes, TEBS has an integrated load function, which can be accessed through a trailer
monitor unit such as that shown in Illustration 2 below. It will show your group axle weights
as well as individual axle weight loading.
Note:
ELECTRICS – GENERAL: ISO 1185 or SAE J560 electrical connectors (AS 4735-2003)
are approved in ADR 42. These should be used for all multi trailer combinations, and are
recommended for all combinations. Wire size and quality, crimping and maintenance are
important, and earth/ground wires should be given the same care and attention as power or
positive wires. Trailer electrical connections have multiple power wires for different functions
but only a single earth wire. A smaller diameter (cross-section) or compromised/damaged
earth wire would render the complete trailer system (lighting and/or ABS/TEBS systems)
non-functional.
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Illustration 2: An example Trailer Monitor unit
Recommendations when specifying EBS
1. Preferably fit 24 volt or multi volt systems to trailers for compatibility with modular
combination above two trailers. Ensure that all trailers are appropriately wired and
fitted with 24 volt EBS plugs
2. Fit base sockets conforming to ISO 7638-1 (24 Volt) or 7638-2 (12 Volt) to both
Prime Mover and Trailers.
3. Ensure that all trailers are fitted with CAN-BUS. If the prime mover is not providing a
CAN signal, speed of brake application can be improved by fitting a signal generator
to the trailer.
4. Fit inverters to 12 volt prime movers and 24 volt power supply to trailers. 12 volt
power supply from the prime mover is possible if no more than two trailers are to be
powered up, and the overall length is no more than 26m. However, 24 volt supply to
the trailers is optimal.
5. The prime advantage of a running multi-volt connection is in long multi-trailer
combinations. Where a 24 volt supply is used at the front, if there is a greater voltage
available than 9 volts at the last trailer, the system will still operate.
6. When determining where to place an inverter to overcome power differences, for
example a 12 volt prime mover supplying a 24 volt trailer, positioning of the inverter is
important. The inverter should be fitted close to the strongest power source, on the
front of the trailer. The closer the inverter is to the power source, the better the result.
Wrongly fitting an inverter too far down the trailer is a common error in B-doubles,
and is fixed by shifting the trailer mounted invertors closer to the front of the trailer.
SHOULD YOU HAVE ANY DOUBTS OR ENQUIRES WHEN CONSIDERING OR USING TEBS, PLEASE DO
NOT HESITATE TO ASK – CONTACT YOUR SUPPLIER. REMEMBER TO INCLUDE YOUR PRIME MOVER
SUPPLIER, AS NOT ALL PRIME MOVER SYSTEMS ARE THE SAME.
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