ABS Braking Requirements (Stage 3)

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Prime Mover Ratings Project Stage 3 Report: ABS Braking Requirements Page





1

Hartwood Consulting Pty Ltd





El ectri cal & Mechani cal Engineering Services

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El ectri cal Safety

El ectromagnetic Compatibi lity

6/39 Wellington Street





Power System Di sturbances

St Kilda 3182 Victoria






Techni cal & Forensi c Investi
gations

Expert Systems & Intel l i gent Manual s

Telephone 03 9510 3882






Fi ni te El ement Modelling

Facsimile 03 9510 3682






Heavy Vehi cl e Braki ng & Dynamics

Mobile 0438 339 413






Vehi cl e Certi fi cation

Speci al ist Vehi cle El ectri cs

pmhart@hartw
ood.com.au






Product Devel opment



Prime Mover Standards Project




ABS Braking Requirements (Stage 3)



By


Peter Hart

Hartwood Consulting Pty Ltd


June 2003






Final Report

Prime Mover Ratings Project Stage 3 Report: ABS Braking Requirements Page





2


1

Summary


The Prime Mover Ratings was instituted to investigate whether u
niform technical
requirements should be applied to all prime
-
movers irrespective of the nature of
application (such as single,
B
-
double

or Road Train configuration). This project,
Stage 3 is concerned with the case for requiring Antilock Braking Sy
stems (ABS) and
with the technical requirements that should apply when ABS is installed on a prime
mover. Because there is substantial overlap in the considerations applying to trailers
and motive vehicles, the project has also investigated the issues conc
erned with use of
ABS on trailers.


Following a review of the previous Australian and US studies into ABS use on heavy
vehicles, a Discussion Paper (which is Appendix 2) was prepared and circulated to
interest groups including the Australian Trucking Assoc
iation, Industry Technical
Council, Truck Industry Council, ABS suppliers and vehicle engineers. This final
report takes account for the comments that were received in response.


The current requirements for ABS on heavy combination trucks in Australia was

determined by inquiries made of all state jurisdictions. With the exception of the
Northern Territory all jurisdictions apply rules 136 and 138 from the Australian
Vehicle Standards Rule 1999. These require that ABS be fitted to a
B
-
double

prime
-
m
over and to trailers in a
B
-
double

that includes a road tank vehicle containing
dangerous goods. Additionally some jurisdictions apply similar requirements to B
-
Triple combinations.


The technical requirements for ABS when it is fitted are in ADRs
35/01 and 38/02.
Four significant changes are suggested to these requirements which are:



Voltage level can be either 12V or 24V;



The ABS be capable of split
-
coefficient performance. That is, each modulator
valve only controls wheels on one side of the vehi
cle;



All wheels on the vehicle be controlled.



The ABS should have veto power over auxiliary
-
retarder controls.


Additionally it is proposed that vehicles with ABS should have automatic brake
adjustment and that the brake release time requirements should be

dropped for ABS
-
fitted trucks.


A suitable technical performance for an ABS is that it be capable of meeting the
Category 1 (motive vehicles) or Category A (trailers) performance levels from ECE
R13.9. Local testing for this should not be required. If the

supplier can evidence an
ECE approval certificate on any heavy vehicle for the stated categories, then the ABS
should be acceptable in Australia.


There is now more than ten years experience of ABS on Australian heavy
combination trucks. The reliability o
f ABS has improved with time as problems have
been identified and resolved. There remains a moderate level of wheel
-
sensor related
problems. Anecdotally these are mainly on trailers and arise predominantly from
sloppy wheel bearings and movement of sensors

in their mounts. There is also a level
Prime Mover Ratings Project Stage 3 Report: ABS Braking Requirements Page





3

of wiring and connector faults. It is possible that earlier perceptions have persisted
despite improvements in reliability. However, roadside check by the Victoria police in
2001 found 30% of
B
-
double

trucks
displayed ABS fault lights. This probably
indicates a 20% loss of the potential benefits from ABS.

(what is this based on?)


The costs and benefits of fitting ABS to combination vehicles have been estimated
using the following assumptions:


Crash Cost Savi
ngs
. The cost of crashes involving heavy vehicles has been
estimated from the Bureau of Transport & Resource Economics (BTRE) year 2000
study of the 1996 Australian fatal and serious crashes. There were 161 fatal crashes
involving heavy articulated vehicle
s, 512 involving serious injuries and another
6092 reported crashes
. Using general estimates of crash costs the author estimates
that the average crash cost for articulated vehicles is $87.4K (1996). The annual
exposure of a truck to crashes can be calcul
ated using the estimated total
kilometers travelled by articulated trucks and the total number of crashes involving
articulated trucks in 1996. The exposures for a truck that travels 100,000 km per
annum are:


Fatal crashes:



0.33%


(1 in 303)

Serious inj
ury crashes:


1.0%


(1 in 100)

All reported crashes:


13.2%


(1 in 8)


It is assumed that use of Antilock brakes on all parts of a heavy articulated truck
will potentially reduce crash cost exposure by 6.1%. This value is taken from the
NRTC’s 1996 study i
nto ABS. It is conservative when compared with the 8% used
by the US Highways Administration in their studies. It was also assumed that a
potential reduction in crash cost exposure of 3.05% will result if ABS is fitted to
the motive vehicle only.


Tyre Wea
r Savings:
It is estimated that the 5% tyre wear savings from ABS use
will occur. For vehicles that travel 100,000 km per annum this amounts to $360 for
a
B
-
double
, $275 for a semi
-
trailer and $720 for an
A
-
double

Road Train. Potential
redu
ctions in suspension wear may also exist but have not been quantified nor
included in the analysis.



(Quoted values are in 2003 dollars unless otherwise indicated)


Weight and Fuel Costs:
The opportunity costs due to payload displacement by the
ABS syst
em is estimated to be $100 per annum for a single and $120 p.a. for a
double combination vehicle that travels 100,000 km per annum. The added fuel
usage attributable to the ABS weight is $10 for a single, $15 for a
B
-
double

and
$20 for a Road Trai
n
A
-
double
.


Maintenance Costs:
Based upon NRTC estimates (1996) the assumed
maintenance costs are $132 p.a. for a prime
-
mover and $153 p.a. for a trailer ABS
system. It is likely that many ABS systems have active (wheel
-
sensor) faults and
that som
e benefits are consequently lost. To test the sensitivity to maintenance
costs, the analysis firstly assumes that half of the above
-
mentioned maintenance
costs are expended and that the crash
-
cost and tyre
-
wear savings benefits are
Prime Mover Ratings Project Stage 3 Report: ABS Braking Requirements Page





4

reduced to 80%. Secondly

the analysis is repeated for full maintenance costs and
full benefits.


Installation Costs:

The installed costs of ABS have reduced
since
the NRTC’s
ABS studies of 1994 and 1996. The cost reductions have occurred because ABS
has been mandated in bo
th Europe and North America so supply efficiencies have
increased. Trailer ABS system costs have also reduced on average because single
modulator valve systems, which have lower costs have been commonly applied.
The average installation costs are assumed t
o be $4,500 for a motive vehicle, $500
for trailer connections and $4,000 for trailer ABS.


The economic analysis shows that an Antilock Braking System has a positive cost
-
benefit on single combinations and a negative cost
-
benefit on
B
-
double

and R
oad
Train
A
-
double

combinations. If ABS is only fitted to the motive vehicle then the
cost
-
benefit of ABS is positive for all types of articulated combinations.


The cost
-
benefits become more favourable on vehicles that travel greater than average

distances. A
B
-
double

that travels 200,000 km for 5 years and 100,000 km for the
following ten years (which is a common application) has close to a break
-
even ABS
cost
-
benefit.


The sensitivity to maintenance costs shows that the cost
-
benefits red
uce when full
maintenance costs are expended (which leads to full potential benefits being realized).
The additional benefits achieved do not outweigh the additional costs.


The main recommendation from the project is that ABS be mandated on all new
prime
-
movers and on all parts of a combination vehicle involving a road tank vehicle
that is carrying dangerous goods. That is, the existing requirements for ABS on a
B
-
double

should be applied generally to all articulated vehicle types.


Since the NRT
C’s investigations into ABS in 1994 and 1996 significant changes in
the ABS ‘climate’ have occurred. ABS is now mandated on new heavy trucks in both
the European Union and North America. It is now common for new prime
-
movers in
Australia to have ABS as sta
ndard fitment. About 60% of new Australian prime
-
movers are sold with ABS. Consequently the installation costs have fallen. There is
now a significant experience of ABS in Australia and may early problems have been
overcome. However, Australia is a hard pr
oving ground for truck systems and the
continuing level of wheel
-
sensor problems reflects the harsh road conditions. The
BTREs estimates of the cost of crashes has been substantially revised upwards and
this has greatly increased the potential benefits fro
m using ABS and is the main factor
in making the economics of ABS more favourable than in the NRTCs studies.


Several commentators have called for urgent revision of Australian Design Rules
35/01 and 38/02 so as to improve the inherent level of brake balan
ce between motive
vehicles and trailers, particularly in the lightly laden state. It is likely for example, that
consistent use of load proportioning brake systems on combination vehicles would
greatly improve the dynamic stability of heavy vehicles under
braking. This study has
only been concerned with ABS and has considered other options for improving heavy
vehicle braking performance. ABS is not a panacea for all braking compatibility
Prime Mover Ratings Project Stage 3 Report: ABS Braking Requirements Page





5

problems on heavy trucks because it only operates when wheels would ot
herwise
lock
-
up. ABS does however, protect against instability that is exacerbated by poor
brake balance and this is particularly useful when the parts of a combination have un
-
coordinated brake systems.




Prime Mover Ratings Project Stage 3 Report: ABS Braking Requirements Page





6

Contents


1

Summary

................................
................................
................................
.................

2

2

Introduction

................................
................................
................................
.............

8

3

Scope of the Study
................................
................................
................................
...

9

4

Methodology

................................
................................
................................
.........

10

5

Theory of ABS Operation

................................
................................
.....................

11

5.1

Tyre
-
Pavement Interaction

................................
................................
................................
..................

11

5.2

Stability Considerations

................................
................................
................................
.......................

13

5.3

Antilock System Configuration

................................
................................
................................
..........

20

5.4

ABS Auxiliary Brake Control
................................
................................
................................
.............

23

5.5

ABS for Road Train Combinations
................................
................................
................................
....

23

5.6

Summary
................................
................................
................................
................................
.................

24

6

Australian Regulatory Requirements

................................
................................
....

24

6.1

Australian Vehicle Standards Rules 1999
................................
................................
.........................

25

6.2

Australian Design Rule Requiremen
ts

................................
................................
..............................

26

6.2.1

Application Requirements
................................
................................
................................
...............

26

6.2.2

Technical Requirements

................................
................................
................................
..................

27

6.2.3

Marking Requirements

................................
................................
................................
....................

27

6.2.4

Performance Requirements
................................
................................
................................
.............

28

6.2.5

Effect on Brake Timing Performance

................................
................................
...........................

28

6.2.6

Other Considerations

................................
................................
................................
.......................

28

6.3

State / Territory Requirements
................................
................................
................................
............

31

6.3.1

Australian Capital Territo
ry
................................
................................
................................
............

31

6.3.2

New South Wales

................................
................................
................................
.............................

31

6.3.3

Northern Territory

................................
................................
................................
............................

31

6.3.4

Western Australia

................................
................................
................................
.............................

31

6.3.5

Queensland

................................
................................
................................
................................
........

31

6.3.6

South Australia
................................
................................
................................
................................
..

32

6.3.7

Tasmania

................................
................................
................................
................................
............

32

6.3.8

Victoria
................................
................................
................................
................................
...............

32

6.4

Summary of Australian Requirements

................................
................................
..............................

32

7

International Perspective

................................
................................
.......................

33

7.1

European Union
................................
................................
................................
................................
.....

33

7.1.1

Requirements
................................
................................
................................
................................
.....

33

7.1.2

Performance Requirements
................................
................................
................................
.............

34

7.2

United States and Canada

................................
................................
................................
....................

37

7.2.1

Rigid
Trucks

................................
................................
................................
................................
......

37

7.2.2

Prime Movers

................................
................................
................................
................................
....

37

7.2.3

Semi
-
Trailers

................................
................................
................................
................................
.....

37

7.2.4

Full Trailers

................................
................................
................................
................................
.......

37

7.2.5

Towing Vehicles
................................
................................
................................
...............................

37

7.2.6

Tr
ailing Vehicles

................................
................................
................................
..............................

38

7.2.7

Test Requirements

................................
................................
................................
............................

38

7.3

New Zealand Requirements

................................
................................
................................
................

38

8

Australian Experience of ABS

................................
................................
..............

39

8.1

Australian Experience

................................
................................
................................
..........................

39

8.2

Summary
................................
................................
................................
................................
.................

41

9

Trends Affecting Braking Performance

................................
................................

42

10

Australian ABS Installation Practices and Costs

................................
...............

45

10.1

Prime
-
Movers

................................
................................
................................
................................
........

45

10.2

Trailers

................................
................................
................................
................................
....................

49

10.3

Summary of ABS System Costs

................................
................................
................................
.........

51

11

Costs and Benefits of ABS

................................
................................
................

52

11.1

Estimates of ABS Effectiveness in Reducing Crash Rates

................................
............................

52

11.2

Heavy Vehicle Crash Rates

................................
................................
................................
.................

55

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7

11.2.1 Australian Articulated Vehicle Crash Rates

................................
................................
.................

55

11.2.2


US Heavy Vehicle Crash Rates

................................
................................
...............................

56

11.2.3


Sum
mary of Crash Rates

................................
................................
................................
...........

57

11.3

Estimates of Heavy Vehicle Crash Costs
................................
................................
..........................

58

11.3.1


Australian Crash Costs

................................
................................
................................
...............

58

11.3.2


US Crash Costs
................................
................................
................................
............................

60

11.3.3


Su
mmary of Crash Costs

................................
................................
................................
...........

60

11.4

Estimates of Articulated Vehicle Population

................................
................................
...................

60

11.5

Tyre Wear Savings
................................
................................
................................
................................

61

11.6

Weight and Fuel Costs

................................
................................
................................
.........................

62

11.7

Mai
ntenance Costs

................................
................................
................................
................................

63

11.8

Reliability Cost

................................
................................
................................
................................
......

64

12

Implementation Options
................................
................................
.....................

65

12.1

Considered Options for ABS Implementation

................................
................................
.................

65

12.1.1

Separate Co
nsideration of a Type of Combination Vehicles
................................
................

65

12.1.2


Status Quo Option
................................
................................
................................
.......................

66

12.1.3


ABS Required on Dangerous Goods Vehicles
................................
................................
.......

66

12.1.4


Cost Benefit Analysis of Three
Options

................................
................................
.................

67

12.2

Cost Benefit Analysis

................................
................................
................................
...........................

68

13

Discussion

................................
................................
................................
.............

73

13.1

Review of Comments Received
................................
................................
................................
..........

73

13.1.1


The Truck Industry Council Submission

................................
................................
................

73

13.1.2


Australian Trucking Association Submission

................................
................................
........

74

13.1.3


Wabco (JD Edwards Pty Ltd) Submission

................................
................................
...........

76

13.2

Response to Comments

................................
................................
................................
........................

79

13.
3

Dangerous Goods Articulated Trucks

................................
................................
...............................

81

13.4

ABS Technical Requirements

................................
................................
................................
.............

81

13.5

ABS Requirements on Different Prime Mover Types

................................
................................
....

83

14

Conclusions

................................
................................
................................
...........

85


Appendix 1

Cost
-
Benefit Data
................................
................................
.....................

88

A1.1

Single Combination Vehicle

................................
................................
................................
...............

88

Case 1

Single Combination: ABS on both prime
-
mover and trailer.

................................
...............

88

Case 2


Single Combinati
on: ABS on both prime
-
mover and trailer.
................................
.............

89

Case 3

Single Combination: ABS on both prime
-
mover and trailer.

................................
...............

9
0

Case 4


ABS on the prime
-
mover only
-

Single combinat ion.

................................
..........................

91

Case 5


ABS on the prime
-
mover only


Single combination
................................
...........................

92

Case 6


Single combination. ABS on both parts

................................
................................
.................

93

A1.2

B
-
double Combination Vehicle

................................
................................
................................
..........

94

Case 7


ABS on all
parts of a B
-
double combination.

................................
................................
........

94

Case 8


ABS on all parts of a B
-
double combination.

................................
................................
........

95

Case 9


ABS on all parts of a B
-
double combination.

................................
................................
........

96

Double Maintenance and
Full Benefits
................................
................................
................................
......

96

Case 10


ABS on the B
-
double prime mover only.

................................
................................
...........

97

Case 11


ABS on the B
-
double prime mover only.

................................
................................
...........

98

Case 12


ABS on a B
-
double prime
-
mover only.

................................
................................
..............

99

Case 13


ABS on all parts of a B
-
double combination.

................................
................................
..

100

A1.3

ABS on Road Trains
................................
................................
................................
...........................

101

Case 14

ABS on all parts of a Road Train double.
................................
................................
..........

101

Case 1
5

ABS on the Prime Mover only of Road Train double.
................................
....................

102


Appendix 2

Discussion Paper

................................
................................
....................

103

Appendix 3

List of Respondents
................................
................................
................

122

Appendix 4 Submission by Truck Industry Coun
cil on ADRs 35 and 38

................

123

Appendix 5

References

................................
................................
..............................

126


Prime Mover Ratings Project Stage 3 Report: ABS Braking Requirements Page





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2

Introduction


The Prime Mover Ratings Project is an element of the NRTC’s third reform agenda
and is being managed by Queensland Transport.
The project aims to investigate the
need for common performance and design standards for prime
-
movers used in semi
-
trailer,
B
-
double

and road train applications and where appropriate to develop
technical proposals for common registration standards
for prime movers in all
Australian jurisdictions. The project was initiated following submissions to the
National Road Transport Commission (NRTC) by the Remote Areas Group (RAG)


There are five independent elements to the Prime Mover Ratings Project whic
h are:



Speed Capability.



Spray Suppression.



Antilock Braking Systems.



Dimensions and Sundry Items.



Prime Mover Ratings (final recommendations)


Antilock Braking Systems (ABS) prevents sustained wheel lock
-
up during braking by
modulating the brake actuation

force in a controlled way to allow wheels to turn.
Recently Electronically Controlled Braking Systems has been developed. ECBS
incorporates ABS as one element. Throughout the paper references to ABS will
encompass the anti
-
skid functionality in ECBS.


Thi
s review is intended to identify the issues and workable options for the use of
antilock braking systems on heavy trucks (ADR category NC). ABS is widely used on
B
-
double

prime
-
movers and the question of what technical standards should be
required
is considered separately from the question of whether ABS should be
mandated. Whilst the project is concerned with prime mover requirements this paper
also considers issues to do with ABS on trailers because many considerations are
common or inter
-
related.


The question of whether mandating antilock brakes on Australian heavy trucks can be
justified has been considered previously by the NRTC

(Anti
-
Lock Braking Systems for
Heavy Vehicles Stages 1 & 2, 1994, 1996,
Refs[14] & [15]). The Ministerial Council
sub
sequently decided that antilock brakes be required on
B
-
double

prime
-
movers and
trailers in a
B
-
double

that includes a road tank vehicle carrying placarded dangerous
goods. Mandatory requirements for ABS on heavy vehicles remain controversi
al and
continue to meet significant opposition from the transport industry. This paper will
hopefully assist industry and regulators to assess the potential benefits and issues with
ABS on heavy trucks so that informed comment and decision making can be ma
de.
There is now a substantial Australian experience of ABS, which has informed this
review.


There are also questions that should be considered about technical and performance
requirements that should be met when ABS is used. The Australian Design Rules
(
ADRs) currently specify some requirements however, these are fairly cursory by
international comparisons. A key goal of the Prime Mover Ratings Review is to
develop proposals for common requirements in all jurisdictions when ABS is used.

Prime Mover Ratings Project Stage 3 Report: ABS Braking Requirements Page





9


This investigati
on contains more technical considerations than were appropriately
included in the previous NRTC studies. Technical considerations about ABS
performance and reliability should be considered here because firstly they are relevant
to the details of potential
design and registration rules and secondly because the
specific concerns that the transport industry has with ABS reliability on Australian
trucks should to be explored.



3

Scope of the Study


Whilst this investigation is mainly concerned with ABS require
ments for prime
movers, the potential operation of ABS on a trailer is contingent upon the prime
-
mover providing electrical power and fault
-
indication circuitry. Heavy truck safety
considerations could also exist when only some parts of a combination vehic
le have
ABS. Therefore it has been decided that the scope of this study will cover the issues
relating to ABS on heavy combination vehicles:


This study is not concerned with ABS requirements for rigid trucks or buses. Because
the focus of the Prime Mover

Standards Projects is on common requirements for new
prime
-
movers, the study will not consider retrofitting of ABS to the existing fleet.


The question of whether ABS should be mandated on some types of heavy vehicles
has a long history of controversy in
Australia. This was studied by the NRTC in 1994
and 1996 (Refs [14] and [15]). To an extent this work revisits the question for
articulated trucks in Chapters 11 and 12.


Important issues exist that relate to the technical standards that should be applied

when ABS is used. Consequently a critique of the Australian Design Rule
requirements is presented in Chapter 6.


Differences in the requirements that apply for ABS on heavy articulated vehicles in
different states and territories is of central interest t
o this study. The main aim of the
Prime Mover Standards Project is to develop proposals for consistent requirements in
all jurisdictions. Section 6.3 presents an analysis of the current situation.


Also of particular interest are the issues arising from op
eration of prime
-
movers in
applications where they swap between Road Train and
B
-
double

applications or
mixed applications involving both A
-

and B
-
Train configurations. Current ABS
requirements are different for various vehicle categories. This mat
ter will be
considered in Chapter 13.




Prime Mover Ratings Project Stage 3 Report: ABS Braking Requirements Page





10


4

Methodology


Following investigation by the author a discussion paper was prepared to promote
industry comment. This paper was reviewed by both the project supervisor and the
project reference group. The Discus
sion Paper (which is Appendix 2) was presented at
the Industry Technical Council meeting held in Canberra on February 24
th
2003. It
was also sent to state road freight associations, truck manufacturer’s associations and
to individuals and firms who were i
dentified by the author as having particular
knowledge, interest and / or experience relevant to heavy vehicle braking
performance.


The author received comments on the project from the respondents listed in Appendix
4. The comments are reviewed in Section

13.1 and have influenced the final report as
described in Section 13.2.



.
Prime Mover Ratings Project Stage 3 Report: ABS Braking Requirements Page





11


5

Theory of ABS Operation


5.1

Tyre
-
Pavement Interaction


Anti
-
Lock Braking Systems are intended to control tyre slip at the tyre
-
pavement
surface. The physics of this interactio
n is complex but an overview is appropriate here
so that the conditions can be identified when ABS is likely to be beneficial to vehicle
dynamic control.


The behaviour of static forces that a tyre can produce during braking are illustrated in
Figure 1. Th
e maximum retardation forces occur when the wheel slip is about 10%.
The ability of a tyre to provide sideways forces (which are stabilizing and
manoeuvring forces) falls off consistently as the wheel slips. The maximum
retardation and sideways forces that

a tyre
-
road interface can supply also falls off with
surface smoothness, water / ice / loose material on the road and as the weight on the
tyre is reduced. (Note that the sideways forces also depend on steer angle, which is
not shown).


For small slip lev
els the tyre maintains rolling contact with the road. If the demanded
braking force exceeds the peak of the applicable curve, the tyre will lock and
sideways control will be lost. For example, a desired force level X can be supplied on
rough pavement but n
ot on smooth pavement.


The maximum retardation force that a tyre can provide is proportional to



x Weight where


is the friction coefficient that describes the interaction between
the tyre and the surface. If a tyre locks at full load with full brakin
g on a


= 0.6
surface, it will lock at about a third of the braking force on this surface when the
weight is reduced to 1/3.


This graph illustrates the behaviour of one wheel on a pavement. When there are
multiple wheels in an axle group the wheel slips
of tyres may differ but each
independently behaves as illustrated. The greater the number of tyres the greater are
the maximum available horizontal forces and the greater the load carrying capacity.


The conventional wisdom is that lock
-
up on some wheels
can be tolerated as long as
at least one wheel on each side in the group has not locked. This wisdom can be re
-
expressed as follows:


Adequate sideways forces to maintain stability can be supplied by the group when
one wheel on each side of the axle group
is rolling.


There will be sharper turns on poor surfaces for which the demanded sideways forces
cannot be provided by one wheel rotating in a group. This is particularly true for a tri
-
axle group in comparison to a tandem group.

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12


Braking / Stability For
ce transmitted from tyre to road
























0 ~10 % slip 100% wheel slip



Wheel slip = 0 % is free wheeling.




100 % is fully locked.




Ma
ximum braking forces occur when wheel slip is about 10%



Figure 1

Illustration of the relationship between tyre slip and friction utilization.


Percentage tyre slip measures the extent to which the tyre is turning
relative to the free running rotational s
peed. For example an 11R22.5
tyre which has free rolling turns of 315 turns / km may turn at 290
turns / km during braking. The wheel slip is about 8%.


Tyre
-
pavement friction level depends upon the road surface roughness,
lubriction / water and the tyre
characteristics.









Rough pavement ~0.8g

Smooth pavement / wet
surface 0.3


0.4 g

Gravel surface 0.2


0.4g

Ice ~ 0.1g

Slide values

Both the longitudinal and the transverse forces that the tyre can transmit to the
road are reduced by: Reduced road friction (wet, greasy, loose, frozen,..)



Reduced tyre fri
ction


(bald, hard compound, patterns, bad pressure..)




Reduced contact pressure

(poor inflation, skipping, unloading,..)

Longitudinal


traction & braking

Transve
rse
-

stability, steering

X

~0.4
4

~0.8
g

Prime Mover Ratings Project Stage 3 Report: ABS Braking Requirements Page





13










Figure 2

Domain of ABS operation. (Courtesy Robert Bosch)



5.2

Stability Considerations


Three dynamic modes of a semi
-
trailer that experiences wheel lock
-
up are shown in
Figure 3. ‘Steer
-
wheel lock
-
up’ is

stable in that the vehicle continues generally
straight ahead however steer
-
ability is lost. Braking effort from the rear wheels tends
to straighten the combination vehicle out.


‘Drive
-
wheel lock
-
up’ can result in jack
-
knife, which is sideways sliding of

the drive
axle group (
prime
-
mover jack
-
knife
) resulting in the vehicle ‘folding up’. The prime
-
mover provides some of the braking retardation for the trailer when it is moderately or
heavily laden. This force is transmitted via the kingpin and it causes
an equal and
Slip

Normalized Braking Force

Extra retardation due to
piling effect

Prime Mover Ratings Project Stage 3 Report: ABS Braking Requirements Page





14

opposite reaction on the prime
-
mover which may produce a twisting moment on it. If
the retardation from the trailer tri
-
axle group is low as a result of poor brake balance
the trailer tends to over
-
ride the prime
-
mover and this exacerbates the

tendency to
jack
-
knife.


If the retardation force from the trailer tri
-
axle group is proportionately strong then the
tendency is to pull the vehicle straight however, this situation will often be associated
with ‘trailer
-
wheel lock
-
up’. If the trailer whe
els lock
-
up the trailer may swing
sideways (
trailer swing
).


On a
B
-
double

combination there are retarding or over
-
riding forces from the
following trailer that can lessen or exacerbate the trailer swing. Severe trailer swing
on the lead
-
trailer ca
uses a
trailer jack
-
knife

mode. As for the semi
-
trailer case the
lead trailer provides some of the retardation for the second trailer and this force is
transmitted via the kingpin on the front trailer. If the brake balance is poor the forces
transmitted vi
a the king pin will be smaller or larger than optimum.


Drive axle jack
-
knife

is a severe dynamic behaviour because it occurs quickly (much
quicker than trailer swing) and is very difficult to correct once started. Many
Australian prime movers have a separ
ate trailer brake control. One reason this is done
is to provide the driver with a control that can increase trailer braking relative to
prime
-
mover braking and so pull the rig straight if a jack
-
knifing tendency exists or
could develop. More generally the

trailer hand
-
piece is used to bias the braking to the
trailer.


To achieve stable and controllable dynamic behaviour during braking an articulated
truck should have a balanced braking distribution and fast application times to the
trailer(s). Because the

weight on a truck is highly variable it is necessary to have load
-
proportioning brakes to achieve acceptable brake balance (see Hart, Ref[9], 2003).
However, in a fleet where some vehicles have load
-
proportioning brakes and some do
not, serious braking in
compatibility will occur when combination vehicles are formed
with some parts having load sensing and some not.


ABS can greatly improve stability on a truck, particularly if the brake balance is poor,
by controlling wheel lock
-
up and thereby allowing th
e tyre to provide lateral stability
forces. Stopping distance may also be shortened if the ABS is installed for

select
-
high

but this is at the expense of stability / cornering forces. A
select high

configuration
senses the wheels that are least likely to l
ock so as to achieve minimum stopping
distances. A
select low

algorithm trades stopping distance for enhanced stability and
simplified system design. Most current systems employ more intelligent control
algorithms


select
-
smart



which allows the wheel wi
th high adhesion to enter a
deeper slip in order to get the wheel with low adhesion closer to the optimum slip.
This produces a better trade
-
off between stopping distance and lateral stability.


A subjective rating of the likely severity of poor heavy tr
uck dynamics that arises
from various axle group lock
-
up events is given in Table 1. It provides a guide to the
relative importance of the control of wheel lock
-
up on the various axle groups. This
consideration is important because ABS is often used only o
n some vehicle parts of a
combination vehicle.

Prime Mover Ratings Project Stage 3 Report: ABS Braking Requirements Page





15


The greatest safety benefits come from controlling the drive
-
wheel lock
-
up and
secondly the wheel lock
-
up on the lead trailer of a
B
-
double
.











Figure 3

Three dynamic modes of a semi
-
trailer
that is experiencing tyre
-
pavement slip or skidding
.



Prime Mover Ratings Project Stage 3 Report: ABS Braking Requirements Page





16


Lock
-
Up
Event

Possible Consequence

Most
Likely
Scenario

Driver
Response

Likelihood

(0


㄰N

Severity

(0
-
10)

Risk Rating

%

(L x S)

Drive
-
axle
group lock
-
up.


Both sides

Sideways wheel slip
leading t
o jack
-
knife.


Movement down camber
of roadway or outwards
on corner.


Lightly
laden. Low
friction.


Probably
uncontrollable
situation




6


Severity: 10


Worst case is
a ‘bob
-
tail’
灲ime m潶er






arive
-
axle
gr潵瀠l潣k
-
u瀠潮 潮e
si摥

martial jack
-
歮if
e causing
change 潦 潲ientation⸠
aiffic畬t t漠c潮tr潬
煵ic歬y

iightly
la摥n⸠

o潡搠
扲潫on u瀠
潮 潮e si摥K

aiffic畬t f潲
the 摲iver t漠
c潮tr潬K



P



peverity R






B
-
摯d扬e

lea搠trailer
wheel l潣欠
潮 扯bh si摥s

pi摥ways wheel sli瀠
lea摩ng t漠ja

-
歮ife⸠


j潶ement 摯dn cam扥r
潦 r潡摷ay 潲 潵twar摳
潮 c潲nerK


iightly
la摥n 潮
l潷
-
friction
surface

lccurs sl潷er
than arive
-
Axle jack
-
歮ife⸠ ariver
may c潲rect 批
releasi湧 the
扲a步sⰠat⁴he
ex灥nse 潦
st潰oing
摩stance⸠





S





peverity R





P
M






















Prime Mover Ratings Project Stage 3 Report: ABS Braking Requirements Page





17

Steer
-
axle
wheel lock
-
up

Vehicle continues
straight. Steering
compromised and this
could is detrimental in
avoidance manoeuvers.

However, A severe brake
application is needed to
lock steer wheels because
forward weight transfer
and cabin/engine we
ight
increase steer
-
tyre
contact pressure.

Lightly
laden on
low friction
surface.

Driver can
modulate
braking effort
at the expense
of stopping
distance.






0.6







Severity: 4





2.4


Semi
-
trailer
tri
-
axle
group.


Lock
-
up of
all wheels on
both sides.



Trailer swing down
camber of roadway or
outwards on corner.

Lightly
laden on
low or
medium
friction
surface.

Occurs slower
than drive
-
axle
jackknife. The
driver may
potentially
control this by
modulating the
braking
effort
at the expense
of stopping
distance.






10






Severity: 4








40

B
-
double

lead trailer
wheel lock
on one side

Partial jack
-
knife causing
change of trailer
orientation.


Lightly
laden on
low
-
friction
surface

Driver may
correct by
mo
dulation at
the expense of
stopping
distance.




3




Severity 2




6

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18

Tri
-
axle lock
-
up on one
side

Partial trailer swing
causing trailer movement
out of lane.

Lightly
laden on
low or
medium
friction
surface

Driver can
control this
event by
modulating the
brakes at the
expense of
stopping
distance.




5




Severity: 1.5







7.5


Table 1

Subjective assessment of the severity and likelihood of various axle lock
-
up events.


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19


When assessing risk it is necessary to estimate both the severity of events and th
e frequency or
likelihood of occurrence. As a general rule the load variation on a prime
-
mover drive
-
axle varies over
a factor of 4:1 between laden and unladen states, whilst a semi
-
trailer tri
-
axle group may experience a
variation of 6:1. A steer axle on

a semi
-
trailer prime
-
mover probably experiences a load variation of
1.3:1. These variations greatly influence the likelihood of occurrence.
Considering the lik
e
lihood
and severity estimates g
iven in Table 1, the subjective
risk
ranking
provides an
ordering of the various wheel lock events.


This analysis shows that drive axle lock up constitutes the gre
atest risk and that trailer
tri
-
axle lock
-
up and
B
-
double

lead
-
trailer axle lock
-
up are also significant risks. The
risks associated with the prime
-
mover and comparable to those of the trailer(s). Based
on Table 1, it will be assumed in the economi
c analysis that the contribution of ABS
to crash avoidance by the prime
-
mover ABS system is equal to that of the trailer ABS
system(s).


Prime Mover Ratings Project Stage 3 Report: ABS Braking Requirements Page





20

5.3

Antilock System Configuration


The purpose of ABS operation is to prevent a controlled wheel from locking
-
up. It
does this by monitoring the wheel speed of
sensed

wheels and predicts when lock
-
up
is imminent. The brake air pressure to the
controlled

wheels is then either held or
released in a controlled way to allow the sensed wheel to turn at optimum wheel slip
spee
d (< 10% slip). Additionally the ABS may disable the auxiliary brake system
(retarder).


There are three elements to a typical ABS system:




The
Electronic Control Module
, which monitors the wheel speed signals,
computes the slip
-
performance on the sensed w
heels and operates the modulator
valves.




The
Wheel Sensors

produce a signal with a frequency proportional to wheel
speed; and




The
Modulator Valve

that is controlled by the ECM to either block the brake air
line to the brake chambers (thereby holding the

brake pressure) or exhaust the
brake line to the chambers (thereby reducing brake effort).


The potential benefits of ABS are:




Improved vehicle stability under braking.



Shorter stopping distances.



Improved driver control when braking on slippery surface
s.



Protection against jack knife.



Reduction in tyre flat spotting


particularly on trailers.


ABS achieves these benefits modifying the braking effort at controlled wheels and
thereby increases the utilization of the available friction and allows tyres to

provide
near optimum braking and lateral (stabilizing) forces


A common ABS scheme for an Australian
B
-
double

is shown in Figure 4.




ABS configurations are described by the number of sensors and the number of
modulator valves on the vehicle. F
or example, a system that has six sensors and four
modulation valves is denoted as 6S / 4M. If the vehicle has six wheels (such as a 6 x
4 prime
-
mover) then it follows that all wheels are sensed but some wheels share
modulation valves.


A 4S / 3M system

has four sensors and three modulation valves. At least one
modulation valve must be controlling wheels on each side.


Prime Mover Ratings Project Stage 3 Report: ABS Braking Requirements Page





21



Figure 4

Typical ABS layout for an Australian
B
-
double
.

All wheels in a group are controlled. Trailer systems are usually eith
er
2S/1M or 2S/2M. 4S/2M, 4S/3M, 6S/3M types are can be used but are
uncommon.



Usually the prime
-
mover ABS has four sensors and four modulation valves (denoted
4S/4M). The one modulation valve controls the drive wheels on each side. Other
systems that c
an be used are 6S/4M (6 sensors and four modulators) and 6S/6M (6
sensors and 6 modulators). The 6S/4M system can produce marginally shorter
stopping distances than a 4S/4M system (Ref[6], p123) whilst the 6S/6M system
ensures that no wheel
-
lock
-
up occurs.



The wheel sensor can be installed either on the front
-

or rear
-
drive axle. This choice
affects the ABS performance if there is substantial load transfer during heavy braking.
Significant load transfers occur to the front when the centre of mass of the t
ruck and
trailer are substantially higher than the wheel level. The ‘physics’ of the suspension
reaction is also important
*
. The usual situation during heavy braking is that the tyres
on the rear drive axle have lower contact pressures with the road than d
o the tyres on
the front drive axle. Consequently the rear
-
axle tyres tend to lock at lower brake
application pressures than do the front
-
drive axle tyres.


If the wheels on the front
-
drive axle are sensed then it is possible that the tyres on the
rear
-
dri
ve axle will lock
-
up during heavy braking causing tyre wear. This
configuration produces the shortest stopping distance but some of the benefits of
reduced tyre wear are lost. Stability benefits are also reduced because the rear
-
axle
tyres are skidding.


If the tyres on the rear axle are sensed then both front
-
drive and rear
-
drive tyres will
be modulated when lock
-
up of the rear
-
drive tyre is imminent . Tyre flat
-
spotting does
not occur because the lock
-
up is prevented at all wheels. However, this is achi
eved by
reducing the brake effort on the front
-
drive axle wheels and so the stopping distance
performance is poorer.

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22

Current generation ABS systems take account of these effects is optimized. Tests
show that the stopping distance of these systems is invar
iably better than for a vehicle
without ABS.


Recommendations* by Buckman (Ref[6], 1998) are that

“On a tandem axle vehicle with a 4S/4M ABS system, it is important to mount
the sensors on the rear axle that is most likely to be lightly laden during a
bra
ke stop. Typically this will be the forward tandem axle in the case of a
vehicle with a mechanical spring suspension. On a vehicle with an air
suspension, the sensors are normally mounted on the rear tandem axle since
this axle is most likely to be more l
ightly loaded and more susceptible to lock
during severe braking”.


* As a general rule air
-
bag suspensions have suspension reactions that throw weight
forward and trailer spring suspensions tend to throw weight backwards.


On 6x2 prime
-
movers (that is wit
h an undriven rear
-
rear axle) the driven axle is
usually sensed. This provides the best stopping distance but with some risk of tyre
flat
-
spotting on the undriven axle. 6S/6M systems are recommended for this case
(Ref[6], p106) but 4S/4M systems are usuall
y installed.


4S / 3M systems that use one modulator for both steer wheels and adopt a select low
strategy for the front
drive

axle are apparently used in the USA but not in Australia
(Ref[6], p108).


Trailer ABS systems can be either 2
-

or 4
-
senso
r systems. In 2
-
sensor (2S/2M and
2S/1M) systems the rear axle of the tri
-
axle group for an air
-
suspension or the front
-
axle for a spring suspension is usually sensed (see Figure 4). Four sensor systems
(4S/2M) are less commonly used. They typically sense

wheels on the front and the
rear axles of a tri
-
axle group. Sensors are not fitted to lift
-
axles.


There is a trend to the use of 2S/1M systems on trailers because one manufacturer
(Bendix) has integrated the modulator and ECM into one value housing whic
h has
resulted in cost reductions. 2S/1M trailer systems are acceptable under the USA (and
Canadian) braking rule FMVSS 121 and are apparently widely used on North
American trailers. It is noted that US semi
-
trailers usually have tandem axle group
whereas
Australian trailers usually have a tri
-
axle group. Commercial changes
currently occurring could see the Bendix 2S/1M system disappear in Australia.


ABS systems are usually optimized for highway use. When a truck stops on a gravel
road there is a tendency

for wheels to routinely lock
-
up and for wedges of material to
build up in front of wheels when they are braked. This action is an important
behaviour that assists stopping (but with no assistance to maintaining lateral
stability). ABS modulation of the b
rakes can cause unacceptably long stopping
distances because the system reacts to and tries to prevent the wedge affect. The effect
is illustrate in Figure 2 (snow).


Some ABS systems have an
off
-
road

function (Ref [6], p111) that applies an altered
contro
l algorithm for vehicle speeds below about 40 km/h and disables the ABS for
Prime Mover Ratings Project Stage 3 Report: ABS Braking Requirements Page





23

speeds below 15 km/h. The
off
-
road

function provides a compromise that produces
acceptable stopping distances (with some wheel lock
-
up at low speeds) and improved
stability at high
er speeds (with wheel lock
-
up prevented). The
off
-
road

mode can be
activated manually or by an interlock with say differential
-
lock selection. Most ABS
systems used in Australia have this feature but it is rarely if ever used. Some
commentators have stated

that current ABS systems do not modulate braking activity
at vehicle speeds below about 15 km/h and that this does allow gravel piling to occur
in the final stages of the stop.


Tests show that the stopping performance of a single combination vehicle with

ABS
properly installed is shorter than a comparable truck without ABS in all situations
other than braking on a loose surface (e.g. a gravel road). Stopping distance
improvement of 16


46% are claimed for a laden semi
-
trailer combination (Ref[6],
p123).
The greatest improvement occurs on ‘split
-
coefficient’ surfaces (when the ABS
has
split
-
mu

configuration).



5.4

ABS Auxiliary Brake Control


ABS systems for motive vehicles usually have a auxiliary brake (retarder) control
function. This disables the ret
arder (if it is
connected
) during ABS intervention. This
feature is provided so that optimum control of wheel slip can be implemented by the
ABS, which is not possible if the retarder is also acting on the drive wheels. It has the
secondary benefit

that it controls retarder
-
induced wheel lock
-
up.


Engine brakes often have the same nominal power rating as the engine. There has
been substantial increase in the rating of these retarders over recent years. If for
example, the prime
-
mover has a 600Hp eng
ine (450 kW at 2100 RPM) then the
engine brake retardation force that is applied to the drive wheels at an assumed engine
speed of 1597 RPM at 100km/h is about 12.2 kN.

[450 kW x 1597/2100 / (55.5 Rad/sec x 0.505m); Overdrive gear 0.78, Differential
rati
o 3.9, Tyre turns/km = 315].


If the truck weighs 15t unladen then this retardation force will produce a 0.08g stop.
This stop corresponds to low service braking effort. Because the retardation forces
only act on the drive wheels, there is likelihood of
wheel lock
-
up on a poor or slippery
surface. If the drive axle weight is 8t in the unladen state then the adhesion utilization
demand is about 0.16. A wheel will lock if the retardation force

/
dynamic weight is at
this level.


ABS will sense drive wheel l
ock
-
up due to retarder action and will both modulate the
braking effort (when the service brakes are applied) and disable the retarder. Because
retarder action is usually automatic once the throttle is relaxed there is a potential
safety benefit if the ABS

having veto control over the auxiliary brakes.


5.5

ABS for Road Train Combinations


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24

ABS has been fitted to a few Road Trains on a trial basis. The trials had 2S/2M
systems on dolly trailers and 4S/2M on the semi
-
trailers. The installations are
complex becaus
e there are many separate ABS systems (one per trailer) and
consequently large numbers of electrical connectors. Because trailer systems must be
supplied at 12V, significant technical problems arise from voltage drops. Two of the
trial installations had sw
itch
-
mode power supplies fitted to achieve adequate voltage
stability.


ABS is unproven on Road Train trailers. It is expensive because of the number of
trailers involved and may suffer unacceptable voltage drops without special electrical
design. It is p
lausible that ABS will improve the dynamic stability of a Road Train.
However, there is inadequate experience of ABS on Road Trains to be certain that
benefits will occur and the technical challenges are great so that reliability is an issue.


5.6

Summary




Anti
-
Lock Braking systems will improve the dynamic stability under braking of a
combination vehicle if the system configuration is well
-
engineered. The benefits
of ABS can be:



Improved vehicle stability under braking. This results because a locked wheel

can provide low lateral stability forces.



Shorter stopping distances.



Improved driver confidence when braking on slippery surfaces.



Protection against jack knife.



Reduction in tyre flat spotting


particularly on trailers.




The main improvement in stabil
ity will come from preventing wheel
-
lock at the
drive axle wheels and at the lead
-
trailer wheels in the case of a
B
-
double
.



Four channel systems (denoted 4S/4M) are usually used on prime
-
movers.



Usual practice is to sense the wheels most likely to

lock (which is the rear axle on
an air
-
suspension and the front
-
axle on a spring suspension).



Trailers now often have 2S/1M systems, which is a relatively new development.
One modulation valve controls all wheels in a tri
-
axle group.



ABS will increase sto
pping distances on gravel roads. Some ABS have an off
-
road
function that alters the operation at lower speeds (< 40 km/h) and allows some
wheel lock to facilitate stopping.



ABS can veto retarder operation. This potentially improves vehicle safety because
m
odern retarders have the potential to lock
-
up drive wheels on slippery surfaces
and under adverse circumstances.



Because of the large number of axle groups on a Road Train together with the
requirement to supply ABS on trailers with 12V power, ABS is unpro
ven on Road
Trains.





6

Australian Regulatory Requirements


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25

Anti
-
Lock brake systems are presently mandated in Australia on two categories of
heavy vehicles:


1

B
-
double

prime
-
movers (first used in a
B
-
double

after 1993) and

2

B
-
double

prime
-
movers and tank trailers when they are carrying dangerous
goods.


State and territory road traffic
/ transport
authorities administer the applicable
regulations. The regulations are based on agreed national heavy vehicle rules that
have been develop
ed by the National Road Transport Commission. The stipulation for
ABS is stated in the
Australian Vehicle Standards Rules 1999

(Rules 13 and 138(3))
and the technical requirements for ABS are in the
Australian Design Rules
.


6.1

Australian Vehicle Standard
s Rules 1999


State and territory legislation governs the in
-
service requirements for vehicles on
public roads. All jurisdictions have agreed to implement the requirements in the
Australian Vehicle Standards Rules 1999

for Anti
-
Lock Brake Systems on heavy
vehicles into their jurisdictional road traffic acts.


The originating requirements are:



Australian Vehicle Standards Rules

1999
,


Division 4 Additional brake requirements for
B
-
double
s and long road trains




136 Braking system design for a pr
ime
-
mover in a
B
-
double


“(2) A prime mover used in a
B
-
double

must also have an anti
-
lock braking system


complying with third edition ADR 64, if the prime mover

(a)

was built after 1989; or

(b)

was first used in a
B
-
double

after 1993;
or

(c)

is used in a
B
-
double

that includes a road tank vehicle containing dangerous
goods. “


and


138 Braking system design for trailers in
B
-
double
s or road trains


(3) A semi
-
trailer, regardless of when it was built must have an antilock bra
king
system

that complies with ADR 38/01, if:


(a)

it is used in a
B
-
double

that includes a road tank vehicle, whether or not the semi
-
trailer is itself a road tank vehicle; and

(b)

the road
-
tank vehicle is carrying dangerous goods.


There is confusion ov
er the definition of a road tank vehicle for dangerous goods
haulage. The Australian Vehicle Standards Rules (1999) has the following definition:

Prime Mover Ratings Project Stage 3 Report: ABS Braking Requirements Page





26

be:

“road tank vehicle

has the same meaning as in the sixth
-
edition of the
Australian Code for the Transport
of Dangerous Goods by Road and Rail.”


The sixth edition of the Australian Dangerous Goods Code defines a road tank vehicle
to be:



“A road vehicle of which a tank forms part or to which a tank is attached.”


(Note that the fifth edition of the Code had a
nother definition that could be understood
to require the tank to be an integral part of the vehicle).


The Code defines a
tank

to be “a receptacle, other than an intermediate bulk
container, having a capacity in excess of 250l for liquids and a capacity i
n excess of
500l for gases.”



The
tank

definition includes a demountable tank; portable tank and a tank container
but seems not to include a drum.


Clearly the definition of a road tank vehicle includes vehicles that have an integral
tank and a tank whic
h is removable. It is not widely understood by industry that ABS
is then on a flat bed trailer in a
B
-
double

that has a demountable tank on it containing
dangerous goods.


6.2

Australian Design Rule Requirements

6.2.1

Application Requirements


The
stipulation that
B
-
double

combination trucks have Antilock Braking Systems first
appeared in the Federal Interstate Regulations that established the Federal Interstate
Registration status for heavy vehicles. This course was apparently taken to forc
e
agreement by state jurisdictions to
B
-
double

configurations on Australian roads.
Because some technical requirements for
B
-
double
s did not form part of the
Australian Design Rules, some states required individual vehicle inspection, testi
ng
and sign off by an authorized engineer, which added about $500 to the cost of each
B
-
double

combination vehicle. To an extent the Prime
-
Mover Ratings project is
attempting to correct the situation.


The technical requirements for ABS that are no
w in the ADRs had their genesis with
Queensland Transport
. Queensland Transport was rightly concerned that inadequate
technical requirements for ABS had been published in the Federal Interstate
Regulations. They publis
hed a statement of technical requirements for application of
ABS to
B
-
double
s in Queensland that was later developed into the requirements now
in ADRs 35, 38 and 64.


The Australian Design Rules apply to vehicles when they are first used in transpo
rt,
which is taken to mean when they are first registered.


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27

ADR 64/00
Heavy Goods Vehicles Used in Road Trains and
B
-
double
s
, is applicable
to NC category heavy vehicles and not to trailers. Clause 64.5.2 requires that a vehicle
designed for use in

a
B
-
double

(that is a prime mover) must have an Anti
-
Lock
Braking system.


B
-
double

prime
-
movers have a particular status in the ADRs. Manufacturers are
required to identify such as prime
-
mover as suitable for
B
-
double

service by p
lating it
as such (ADR 61/00 Cl 8.1.3). A
B
-
double

prime
-
mover must comply with ADR
64/00 requirements and so must have an ABS if it is plated as suitable for
B
-
double

service. Note that B
-
Triples have no particular status in the ADRs and f
all into the
Road Train category.


There is no ADR stipulation that a trailer for
B
-
double

service have ABS.


6.2.2

Technical Requirements

The technical requirements for ABS systems when fitted to new vehicles are specified
in ADR 35/01
Commercial

Vehicle Braking Systems

and ADR 38/02
Trailer Brake
Systems.


Both rules specify that
when

ABS is used:



It must be used on every axle group.



For a trailer with a tri
-
axle group, ABS must control at least two axles in the
group.



For a tandem axle group,
ABS must be fitted to at least one axle in the group.


The electrical requirements for the ABS system are:



When fitted to a semi
-
trailer, the electrical connections between prime
-
mover
and semi
-
trailers must be 12V powered.



The electrical connector between

prime
-
mover and semi
-
trailer and between
semi
-
trailers is to be DIN 72570 (12V) and the pole allocations are as specified
in the rules.



A yellow warning light must come on in the cabin when the circuit through pole
5 of the connector is grounded.



Separate

power supply and return circuits are required for the modulation valves
(30A capacity) and the control unit (4A).



A disruption to the electrical power supply of a trailer anti
-
lock system must
cause pole 5 to be connected to ground.



The prime
-
mover must h
ave a red light to warn of ABS failure on this vehicle.


6.2.3

Marking Requirements

Category TC and TD trailers “designed for use in a
B
-
double

and fitted with Antilock
Brakes in accord with ADR 38/01” must be plated with the words “THIS TRAILER
I
S FITTED WITH AN ANTI
-
LOCK BRAKING SYSTEM COMPLYING WITH
ADR 38/01”


This requirement seems to mainly affect a
B
-
double

lead trailer because it is dedicated
to
B
-
double

(or B
-
Triple) service. A semi
-
trailer that has ABS brakes and that may
be
Prime Mover Ratings Project Stage 3 Report: ABS Braking Requirements Page





28

used in a
B
-
double

or in a single combination will probably not be placarded as it is
not a dedicated
B
-
double

trailer.


6.2.4

Performance Requirements

When a new motive vehicle has an Anti
-
Lock brake system fitted the manufacturer is
re
quired to certify that the service brake system:




Meets ADR 35/01 full level requirements (3.78 m/s
2
from 100 km/h
,

Items 3
and 6, Table 1) and the service brake compatibility tests (Cl 35/02, 8.18) with
the ABS operational; and



Meets ADR 35/01 partial fa
ilure requirements (1.78 m/s
2

from 40 km/h, Item 5
Table 1) with the ABS disabled.


ADR 38/02 does not specify whether the stopping tests should be conducted with the
trailer ABS system active or not.


Additionally both ADRs 35/01 and 38/02 require that an

axle that has ABS fitted will
not lock when the vehicle is heavily braked from initial speeds of 40 km/h and 80
km/h in both the fully laden and lightly laden cases. This performance is to be
maintained whilst the vehicle speed is greater than 15 km/h. Th
e test is to be done on
a surface that has approximately the same road friction on both sides (i.e. not a
split
-
coefficient surface
) of the vehicle.


Brief periods of wheel lock are acceptable during the operation of the anti
-
lock system
(i.e. modulation o
f the braking activity) but stability must not be affected.


6.2.5

Effect on Brake Timing Performance

As discussed in Section 5.3 Anti
-
Lock Brake System modulation valves are installed
just prior to the brake chambers. They affect the application and relea
se timing to the
brake chambers by adding to the pneumatic
-
flow resistance. In particular the release
timing can be adversely affected. This adds to the challenge to achieve acceptable
brake release times (considering that Australia has the world’s most st
ringent brake
release time requirements


See ADR 35/01, 8.17.5 ADR 38/02, 22.2.7 )


It is unwise to install quick release valves on the delivery side of an ABS modulation
valve because the ABS is programmed for an assumed chamber exhaust
characteristic.

Therefore the brake engineer must ensure that the pneumatic
restriction of the ABS valve is minimal and that the release timing performance of the
affected brake circuit is good.


6.2.6

Other Considerations

Antilock Brake systems probably exhaust brake ch
amber air pressure with each
modulation cycle. Consequently higher than usual air usage occurs when the ABS is
active. ADR 35 prescribes the minimum air capacity of a prime mover (total available
tank volume to be greater than twelve times chamber volume p
lus an allowance for
Prime Mover Ratings Project Stage 3 Report: ABS Braking Requirements Page





29

the trailer usage) and ADR 38 of that of a trailer (total available tank volume to be
greater than eight times chamber volume).


No additional air tank requirement exists for a vehicle fitted with ABS. To minimize
air usage some truck

manufacturers fit automatic slack adjusters to ensure that the
brakes are always in good adjustment and thereby minimize air usage and reduce the
modulation time periods. This is not mandatory. ABS suppliers generally recommend
that auto slack adjusters b
e used with ABS.


Prime mover ABS units have the capability to over
-
ride the retarder. This is
recommended practice so that the ABS can provide optimum control of wheel slip
without the (uncontrolled) application of retarder wheel forces. The ADR’s are si
lent
about this.


The Australian Design Rules recognise three categories of heavy vehicle combination
types, which are:




A Road Train comprising a combination vehicle, other than a
B
-
double

consisting of a motor vehicle pulling at least two trailer
s (counting as one
trailer a Converter Dolly supporting a semi
-
trailer)




B
-
double

a combination vehicle consisting of a prime
-
movers towing two
semi
-
trailers; and




A single combination vehicle is by implication a combination vehicle
consisting of
a Prime Mover and one semi
-
trailer.


A Prime
-
Mover is a motor vehicle built to tow a semi
-
trailer. Three types are
recognized by the ADRs, which are a Road Train prime
-
mover, a
B
-
double

prime
-
mover, and by default, a prime
-
mover for a single combin
ation vehicle. The
manufacturer is to identify a Road Train and
B
-
double

prime
-
mover by marking such
on a vehicle identification plate (ADR 61/02, Cl 8.1.3). One prime
-
mover can be both
rated for
B
-
double

and Road Train service.


A Semi
-
Tra
iler is a trailer that has an axle group or single axle towards the rear and a
means of attachment to a Prime Mover that would result in some of the weight being
imposed on the prime
-
mover.


Some jurisdictions allow other (Road Train) vehicle types to oper
ate under permit.
These include:




B
-
Triple consisting of three trailers in a B
-
train configuration; and