Function
There is one key difference between stability control and ABS worth
noting. Stability control utilises a range of sensors to play an active role in
managing road situations before they deteriorate. In contrast, ABS reacts after
the wheel has lost traction by applying an intervention to the wheels to
recover traction.
Stability Control (SC) systems are proactive, taking information from a
range of sources, independent of the driver's knowledge, and acting to
progressively slow the vehicle to regain control. As a result, SC reduces the
likelihood of a roll over or jack-knifing event.
A great example of ESC in action is brought to us by ZF WABCO in the video below. Each manufacturer has their own system - somtimes even named slightly differently [(see Bendix Electronic Stability Program (ESP)], but they share many things.
There are two levels of stability control:
Full or Electronic/Enhanced Stability Control (ESC) includes roll over
control and directional control. The system proactively responds to inputs from
the steering wheel angle, lateral acceleration, and yaw rate sensors with the
capability to brake wheel groups independently to maintain direction control
and reduce the likelihood of a roll over. ESC uses a range of progressive
interventions to manage situations: from de-powering the engine, through to
application of the two brake systems; commencing with the auxiliary brake
(retarders/engine/exhaust), and service brake (truck and trailer).
ESC is only found on powered vehicles that have a steering wheel such as prime movers and rigid vehicles. Combinations where the prime mover has ESC and its trailers have TEBS, are as a whole, considered to have full ESC function as the electronic brake controllers of the truck and trailers work in unison to provide the ESC function for the entire combination.
These interventions have the capability to:
·
straighten
the vehicle to prevent jack knifing
·
manage
over and under steer situations
·
slow
the vehicle or combination that is close to its roll over point.
Roll stability control (RSC) system monitors the lateral acceleration
and wheel speed. It is the only stability control option for trailers, when the
trailer is only receiving power to its TEBS and no other electronic control
(CAN) signal. That is, it is being hauled by a prime mover without an EBS. The
RSC continuously checks and calculates the vehicle’s lateral acceleration and
compares it to the critical threshold at which point rollover may occur. When
the critical threshold is exceeded, the roll stability function intervenes to
slow the vehicle.
Depending on the system setup, RSC may take one or more of the following
actions:
·
start
to slow the unit by reducing engine torque and engaging the engine retarder
·
automatically
apply the braking systems (vehicle and/or the trailer)
Combinations where the prime
mover has ESC and its trailers have TEBS, are as a whole, considered to have
full ESC function as the electronic brake controllers of the truck and trailers
work in unison to provide the ESC function for the entire combination.
The above is dependent on how quickly the critical tipping point is
approaching. Frequently, the system’s activation takes place before the driver
is aware it is needed and thus prevents a catastrophic incident.
SAF Holland (formerly Bendix) provide a great animated example below on how the vehicle
communicates with their Electronic Safety Program (ESP), their own form of
electronic stability control.
Function (More information)
TEBS
must be configured by a qualified professional. On a new trailer, this is done
by the trailer manufacturer prior to delivery. If the trailer has
modifications done to it after initial delivery, such as suspension, different
tyre diameters or a significant change in the trailer load type and its use,
the TEBS will need recalibrating. This must be done suitable qualified
professional.
For maximum benefit, the TEBS unit
located on the truck should be provided with a Controller Area Network (CAN)
connection (ISO 7638 compliant ABS/EBS lead with 7 pins).
For both motor vehicle stability
control and Advanced Emergency Braking (for further information please see the
dedicated chapter), the systems fall into 1 of 2 industry markets:
1. vacuum/air over hydraulic brakes for light/medium
trucks
2. full air brake systems for medium/heavy trucks.
For light/medium trucks with either
vacuum/air over hydraulic brake systems, there are a range of suppliers with
the technology who also provide the technology in the light vehicle
sector, such as Bosch and Denso. The Original Equipment Manufacturers
(OEM) have proprietary service tools and systems to manage and support their
systems. Due to higher production volumes, and model standardisation, these
systems are often specifically calibrated to suit each OEM’s preferences.
Consequently, they are usually re-branded as the OEMs own, and they are totally
responsible for it’s configuration.
For medium/heavy trucks with full air
brakes, the segment has 3 technology providers for the 16-truck OEMs brands
being ZF-Wabco, Knorr -Bremse and SAF Holland. The OEMs will tailor the
stability system to suit their brand and they will have propriety access to the
system settings. Additionally, these full stability systems can be
supplied as either an ABS or EBS platform-based.
The
electronic braking system platforms, typical of European based trucks, provides a direct Controller Area Network (CAN)
communication of key parameters to support the full functionality of electronic
systems on a TEBS equipped trailer. The ABS platform-based stability
control system, typical of North American based trucks does not. However,
the vehicle can be fitted with a separate independent Trailer Response Management
(TRM) system which will produce a one-way brake activation signal to
the Trailer Electronic Braking System (TEBS) to apply the trailer brakes.
Both approaches; the EBS and ABS
platforms for stability and AEB will meet the ADR and significantly improve
vehicle safety outcomes.
Having an EBS equipped truck does not
necessarily guarantee all advanced features that were not mandated at the time
of the vehicle manufacture, are present. For example, as of September 2022,
several Advanced Emergency Braking systems are still not mandatory, such as
lane departure assist and autonomous emergency braking. Purchasers need to
check with their vehicle supplier as to what functions are included as standard
fit. Purchasers need to be aware that non mandatory functions may need to be
requested as an add-on.
The leading suppliers of Trailer
electronic brake systems in Australia are SAF Holland, Knorr-Bremse and
ZF-Wabco. These systems provide for full system functionality including brake
activation and faster braking force requests via wire. They are generally
called Trailer EBS or TEBS. ABS, load sensing and anti-roll functions on a
trailer will be available even if the trailer is hauled by a prime mover
without EBS, provided that the trailer receives electrical power from the prime
mover. Retro fitting a complaint EBS connector to the prime mover that only has
the power and earth pins active, provides a low cost and significant step up in
safety for the combination. Reducing the likely hood of jack knifing (through
ABS and load sensing on trailer ) and roll over (through anti-roll function on
trailer).
Sometimes and inappropriately, trailers
with advanced braking systems are not connected! It is a legal requirement,
where the facility exists to connect the prime mover to the trailer’s TEBS,
they must be connected and powered. Refer to NHVR’s vehicle standards guide
number 25 (VSG25) for further information.
As a fall-back position, particularly
in a mixed fleet or where the trailer is behind a subcontractor’s truck, modern
multi volt TEBS units can be powered almost instantaneously through the brake
light circuit. This however does NOT provide full anti-roll functionality, but
will establish ABS functionality that will prevent gross wheel lockup of the
trailer.
Truck and trailer connectivity
The following are useful points to note about some of the
hazards when dealing with truck/trailer connectivity.
- In some cases, the trucks stability system may be
de-activated when towing e.g., the supplier configuration does not allow this,
or the system has two different parameter sets – one for towing and one when it
is not towing. This change to the parameter set is generally managed by the
OEM’s electrical wiring/connectors for towing.
- Roll coupled trailers are joined or linked via a 5th wheel
(i.e., B type coupling on a semi-trailer or B Double) and can manage the roll
event for the linked combination and vice versa. Non roll coupled truck and
trailer (i.e., A type couplings typically used with draw bars and converter
dollies), the combination elements should both have the stability control
functions. In a combination where a number of trailers are used and not all
have TEBS fitted, combining the trailers in the correct arrangement is crucial.
Poor arrangement of trailers in these cases may lead to worse brake performance
than if all trailers had no TEBS. Industry has developed guidelines as to which
order trailers should be connected in. This is outlined in the “Guide
to Stability and Performance for Heavy Vehicle Combinations”. Following this guide will maximise the
combination’s brake performance given the equipment at hand.
Australian Design Rules (ADR)
For trailers, ADR38/05 mandated Roll Stability Control (RSC) from the 1st November 2019 and requires all heavy trailers (ATM greater than 4.5tonne), except dollies and special trailers with more than four axles in a group or four wheels in a row where ABS only) to be fitted with RSC.
For trucks, ADR35/06 mandated Electronic Stability Control (ESC) for prime movers with either 2 or 3 axles plus short wheelbase rigids with either 2 or 3 axles from 1st January 2022.
For trucks with long wheelbase rigids with either 2 or 3 axles, ESC will be mandated by ADR35/07 from 1 January 202X?? TBC! This aligns with the introduction of AEB Advanced Emergency Braking.
Further information and issues
Truck and trailer stability systems operate independently of the driver and won’t stop operating until the systems believe it is safe to do so. The driver won’t receive any warning of their activation. They may experience a loss of throttle response, engine brake activation or service brake activation! Some systems provide the driver information ideogram on the cluster to advise of “ESP”, “ASR”, “EBS” intervention.
When stability control is available, at key on, the systems will assume a laden vehicle condition with a resulting aggressive braking approach. Within a few stops/corners/7 gear changes/seconds, the system will learn the vehicle's mass from engine torque demand and for electronic controlled suspension loading feedback.
Each OEM system is developed to comply with ADR and each OEM system being unique with unique setups and installations.
Retrofitting trailer brakes.
Some trucks when not provided with trailer brake capability from the OEM
at purchase, may not have stability control functioning for the trailer when
the trailer is attached. These trucks are capable of towing a trailer with TEBS,
however, for the system to work, it needs to be configured by the truck OEM.
While a trailer is attached and the truck does not have the function
switched on by the OEM, the truck’s ESC system may be temporarily de-activated.
If retrofitting trailer brake kit to a rigid unit, check with the system
installer to clarify the installations operational parameters.
Ideally, the truck/trailer combination fitted with the new technology
should be taken to your OEM for correct set up.
In multi combination vehicles, the trailers tend
to roll before the truck. ADR 38/05 requires
anti roll control to be fitted to each trailer with the exception of dollies.
However, dollies are still required to be ABS equipped.
Attention
Because of the autonomous operation of the ESC system, which may brake aggressive, for maximum safety and overall system performance, the trailer should be fitted with at least ABS capability.
For further information on Trailer/Truck brake compatibility, your OEM supplier should be your first point of contact, but for heavy trucks and trailers – Haldex, Knorr- -Bremse/Bendix and ZF-Wabco can provide a beneficial second opinion.
For these compatibility issues, refer to the industry developed guide: Braking Advisory ARTSA
The system does not rely on any external system inputs, just the vehicle’s sensors and vehicle speed
System Modifications
In each case, what is a permissible modification and what
is prohibited, will be at the discretion of an
appropriate qualified AVE (Authorised Vehicle Examiner) potentially with guidance
provided by the OEM.
ADR compliance and certification
testing is often a small part of the EBS system’s configuration and
development. Testing is done for a range of conditions and vehicle options:
- Laden and unladen with appropriate vehicle weight
distribution and body fitment
- Rigid towing, non-towing vehicles and tractors
- For a set of wheelbases limits
- For a range of load Centre of Gravities (CoGs)
- Brake system types – brake chambers sizers, disc vs drums,
S vs Z cam brakes
- Suspension/wheels-tyres combinations
- Number of axles
- Steering geometry
- Foundation brake system components – valves and air lines
ALWAYS CONSULT THE OEM, QUALIFIED AVE OR SYSTEM SUPPLIER, IF IN DOUBT
Technology is evolving quickly, and equally so is stability control system’s intelligence with its ability to adapt and adjust to changes.