Road vehicles -- Test of vehicle air braking systems with a permissible mass of over 3,5 t -- Acquisition and use of reference values using a roller brake tester

ISO 21995:2008 provides a method for the acquisition of suitable braking reference values that the manufacturer is required to provide, and for the use of these reference values in periodical technical inspection (PTI) on air brake systems.

Véhicules routiers -- Essais des systèmes de freinage à air comprimé des véhicules de masse admissible de plus de 3,5 t -- Acquisition et utilisation des valeurs de référence en utilisant un banc de freinage à rouleaux

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Published
Publication Date
03-Mar-2008
Current Stage
9020 - International Standard under periodical review
Start Date
15-Oct-2021
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ISO 21995:2008 - Road vehicles -- Test of vehicle air braking systems with a permissible mass of over 3,5 t -- Acquisition and use of reference values using a roller brake tester
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INTERNATIONAL ISO
STANDARD 21995
First edition
2008-03-15
Road vehicles — Test of vehicle air
braking systems with a permissible mass
of over 3,5 t — Acquisition and use of
reference values using a roller brake
tester
Véhicules routiers — Essais des systèmes de freinage à air comprimé
des véhicules de masse admissible de plus de 3,5 t — Acquisition et
utilisation des valeurs de référence en utilisant un banc de freinage à
rouleaux
Reference number
ISO 21995:2008(E)
ISO 2008
---------------------- Page: 1 ----------------------
ISO 21995:2008(E)
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© ISO 2008

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ii © ISO 2008 – All rights reserved
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ISO 21995:2008(E)
Contents Page

Foreword............................................................................................................................................................ iv

Introduction ........................................................................................................................................................ v

1 Scope ..................................................................................................................................................... 1

2 Normative references ........................................................................................................................... 1

3 Terms, definitions and symbols.......................................................................................................... 1

3.1 Terms and definitions........................................................................................................................... 1

3.2 Symbols ................................................................................................................................................. 3

4 Acquisition method .............................................................................................................................. 3

5 Use of reference values for testing on roller brake testers.............................................................. 7

6 Data acquisition and distribution by the vehicle manufacturers..................................................... 7

7 Documentation of results and evaluation .......................................................................................... 7

Annex A (informative) Examples ...................................................................................................................... 8

Bibliography ..................................................................................................................................................... 13

© ISO 2008 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO 21995:2008(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies

(ISO member bodies). The work of preparing International Standards is normally carried out through ISO

technical committees. Each member body interested in a subject for which a technical committee has been

established has the right to be represented on that committee. International organizations, governmental and

non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the

International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of technical committees is to prepare International Standards. Draft International Standards

adopted by the technical committees are circulated to the member bodies for voting. Publication as an

International Standard requires approval by at least 75 % of the member bodies casting a vote.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. ISO shall not be held responsible for identifying any or all such patent rights.

ISO 21995 was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 2, Braking

systems and equipment.
iv © ISO 2008 – All rights reserved
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ISO 21995:2008(E)
Introduction

UNECE Regulation No.13, paragraph 5.1.4.6 (on reference braking forces) requires, as part of the type

approval process, that the manufacturer provides the Type 0 braking performance figures as reference values

arranged in a tabular or graphical form.

The purpose of reference values is to make adequate data available for conducting periodical vehicle tests,

which are most easily performed on roller test benches. Within Council Directive 96/96/EC, testing in service

is required to achieve a heavy truck brake efficiency of at least 45 %, and this can be performed by road

testing or, more conveniently, on roller brake test benches. The roller brake tests are based on the available

reference values declared by the vehicle manufacturer at type approval.
NOTE The minimum requirements are:

⎯ 50 % in the case of vehicles of categories M2, M3, N2, N3, O3 and O4, except semi-trailers;

⎯ 45 % in the case of semi-trailers.

This International Standard provides a procedure for testing both motor vehicles and trailers in service to the

level of performance required for periodical technical inspection (PTI).

It is possible that the values will need adjustment to reflect national or international in-service requirements.

© ISO 2008 – All rights reserved v
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INTERNATIONAL STANDARD ISO 21995:2008(E)
Road vehicles — Test of vehicle air braking systems with a
permissible mass of over 3,5 t — Acquisition and use of
reference values using a roller brake tester
1 Scope

This International Standard provides a method for the acquisition of suitable braking reference values that the

manufacturer is required to provide, and for the use of these reference values in periodical technical

inspection (PTI) on air brake systems.
2 Normative references

The following referenced documents are indispensable for the application of this document. For dated

references, only the edition cited applies. For undated references, the latest edition of the referenced

document (including any amendments) applies.

UNECE Regulation No.13, Rev. 6, 2008, Uniform provisions concerning the approval of vehicles of categories

M, N and O with regard to braking
3 Terms, definitions and symbols
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1.1
braking system

combination of parts which either progressively reduces the speed of the moving vehicle, or brings the vehicle

to a halt and/or holds it stationary, or fulfils both functions
3.1.2
brake

part of a braking system (3.1.1) in which the forces opposing the movement, or tendency to movement, of

the vehicle are developed
3.1.3
braking force

force at the contact surface between a wheel and the ground, produced by the effect of a braking system,

which opposes the rotation of the wheel or the tendency for movement of the vehicle

NOTE The force between the tyre and the rotating roller, produced at the circumference of the tyre during braking,

opposes the force generated at the interface by the roller brake tester attempting to cause continuing rotation of the wheel.

3.1.4
total braking force
sum of the braking forces at all wheels of a vehicle
© ISO 2008 – All rights reserved 1
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ISO 21995:2008(E)
3.1.5
reference braking force

braking forces of each axle generated at the circumference of the tyre on a roller brake tester, relative to brake

actuator pressure
3.1.6
braking force distribution
ratio between the braking force of each axle and the total braking force
3.1.7
total normal force

vertical force, corresponding to the total static mass on the axles of the vehicle

3.1.8
braking rate

ratio between the instantaneous deceleration of the vehicle, a, and the acceleration due to gravity, g, where

only braking forces can be measured
NOTE 1 This ratio is not applicable to semi-trailers.

NOTE 2 Where a cannot be measured, the braking rate, z, is the ratio between the total braking force, F , and the total

normal force, G , corresponding to the maximum loading vehicle weight.
3.1.9
roller brake tester

measuring machine consisting of two pairs of powered rollers used for the assessment of a vehicle’s braking

performance
3.1.10
guaranteed maximum cylinder pressure

pressure of the actuating fluid in the brake cylinder, resulting from full actuation of the brake pedal with the

supply at the cut-in pressure
3.1.11
brake threshold pressure

brake chamber pressure at the intersection of brake force and pressure line (at force = 0 N) in the

force–pressure diagram
2 © ISO 2008 – All rights reserved
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ISO 21995:2008(E)
3.2 Symbols
Symbol Definition Unit
a instantaneous deceleration of vehicle m/s
F total braking force corresponding to maximum loading vehicle weight N
F total braking force needed to achieve z N
f,min min
F braking force of axle i at cylinder pressure p needed to achieve z N
Ni N min
F braking force of axle i at cylinder pressure p N
Ri N
F sum of all F on all axles N
∑ Ri Ri

F reference braking force of axle i suitable for PTI (i.e. at corresponding p level) N

RiPTI A
g acceleration due to gravity m/s
G total normal force corresponding to maximum loading vehicle weight N
p brake actuator/cylinder pressure kPa
p guaranteed maximum brake actuator/cylinder pressure kPa
p brake actuator/cylinder pressure of axle i for calculated PTI value kPa
p brake threshold pressure of axle i kPa
z braking rate —
z minimum demanded deceleration in relation to total normal force at PTI —
min

As declared by the manufacturer in accordance with UNECE Regulation No.13, paragraph 5.1.4.6.

100 kPa = 1 bar.
4 Acquisition method

4.1 At type approval it is impossible to test every version of a particular vehicle range. Consequently, the

vehicle manufacturer chooses a “worst case” vehicle to be covered on the type approval certificate. This

means that the certificate will then include many variants of the tested vehicle, provided that they all have the

same braking system.

In a Type 0 test, a modern heavy vehicle with an electronic braking system (EBS) and disc brakes normally

2 2

achieves a deceleration of 6,0 m/s , whereas the minimum requirement is 5,0 m/s .

4.2 The brake force distribution involves both the static and dynamic brake force distribution. The static

distribution is the result of the different dimensioning of the brakes at the different axles (e.g. different brake

and actuating cylinder diameters). The dynamic distribution is the result of the brake pressure distribution

adjustments during braking. The static distribution is theoretically constant in all situations (excluding the

variation of the friction coefficient of brake pads, which is one of the parameters under assessment). This can

be seen as the different gr
...

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