ISO 21069-2:2008

INTERNATIONAL ISO
STANDARD 21069-2
First edition
2008-05-01
Road vehicles — Test of braking systems
on vehicles with a maximum authorized
total mass of over 3,5 t using a roller
brake tester —
Part 2:
Air over hydraulic and purely hydraulic
braking systems
Véhicules routiers — Essai des systèmes de freinage des véhicules
ayant une masse totale maximale autorisée supérieure à 3,5 t effectué
sur banc d'essai de freinage à rouleaux —
Partie 2: Systèmes de freinage hydropneumatique et purement
hydraulique
Reference number
©
ISO 2008
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but
shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In
the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.

©  ISO 2008
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2008 – All rights reserved

Contents Page
Foreword. iv
Introduction . v
1 Scope .1
2 Terms and definitions .1
3 Symbols .2
4 Test conditions and evaluations.3
4.1 General.3
4.2 Preparation of vehicle and roller brake tester .3
4.3 Calculation and evaluation of test data.3
4.4 Presentation of results.6
Annex A (normative) Technical requirements of roller brake tester .8
Annex B (informative) Periodic inspection of equipment and its documentation .12
Bibliography .14

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 21069-2 was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 2, Braking
systems and equipment.
ISO 21069 consists of the following parts, under the general title Road vehicles — Test of braking systems on
vehicles with a maximum authorized total mass of over 3,5 t using a roller brake tester:
⎯ Part 1: Pneumatic braking systems
⎯ Part 2: Air over hydraulic and purely hydraulic braking systems
iv © ISO 2008 – All rights reserved

Introduction
At present, UNECE Regulation No. 13 covers only some aspects of the periodic technical inspection of
vehicles in use.
In order to fulfil the requirements of UNECE Regulation No. 13, paragraph 5.1.4, this part of ISO 21069 is
designed to cover the periodic measurement of braking performance of vehicles in service.
This part of ISO 21069 specifies the test method whereby a roller brake tester is used to measure, evaluate
and record the braking efficiency of road vehicles of categories M2, M3, N2, N3, O3 and O4 [as defined in
UNECE Consolidated Resolution on the Construction of Vehicles (R.E.3.)] which are equipped with full power
air over hydraulic or purely hydraulic braking systems. This part of ISO 21069 is also applicable for electronic
braking systems (EBS).
INTERNATIONAL STANDARD ISO 21069-2:2008(E)

Road vehicles — Test of braking systems on vehicles with
a maximum authorized total mass of over 3,5 t using a roller
brake tester —
Part 2:
Air over hydraulic and purely hydraulic braking systems
1 Scope
This part of ISO 21069 describes a procedure that generates comparable measurement results in roller brake
testing, such that the efficiency of the service braking system can be assessed reliably wherever the roller
brake tests are performed.
The following items are covered in this part of ISO 21069:
⎯ symbols and definitions;
⎯ test methods;
⎯ test conditions;
⎯ test equipment required;
⎯ accuracy of test equipment;
⎯ data recording and calculation needed;
⎯ presentation of results;
⎯ assessment criteria for pass/fail.
The procedure described in this part of ISO 21069 is not applicable to passenger cars.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
braking force
force between the tyre and the rotating roller, produced at the circumference of the tyre during braking, which
opposes the force generated at that interface by the roller brake tester in order to cause a rotation of the
wheel
2.2
braking force imbalance
difference in the braking forces, measured with running wheels, between brakes on an axle
NOTE Braking force imbalance is expressed as a percentage of the higher force.
2.3
braking force variation
difference between the maximum and minimum values of the braking force, measured over a single wheel
revolution with a constant actuation force
NOTE Braking force variation is expressed as a percentage of the higher force.
2.4
roller brake tester
measuring machine consisting of two pairs of powered rollers used for the assessment of a vehicle's braking
performance
NOTE The assessment is made by measuring the braking force between tyres and drive rollers for each wheel/twin
wheel, either simultaneously or independently, while the wheels of the vehicle axle are being driven and supported by
rollers.
3 Symbols
Table 1 — General symbols
Symbol Definition Unit
F extrapolated braking forces at brake actuator pressure p N
Bi A,ladi
sum of all F on all axles
F
N
∑ Bi Bi
F braking force at the circumference of tyres on axle i at brake actuator pressure p N
Hi A,Hi
F braking force at the circumference of tyres on axle i N
i
F braking force at the circumference of tyres on axle i at brake actuator pressure p N
Li A,Li
total normal static reaction of road surface on all wheels of the individual motor vehicle,
F N
M
or corresponding to F
i
F maximum permissible F N
M,max M
F total normal static reaction of road surface on all wheels of the individual trailer vehicle N
R
F maximum permissible normal static reaction of fully laden trailer vehicle N
R,max
p brake actuator pressure kPa
A
p high applicable brake actuator pressure on axle i kPa
A,Hi
p design brake actuator pressure of laden vehicle on axle i (for extrapolation purposes) kPa
A,ladi
p low brake actuator pressure on axle i kPa
A,Li
R ratio at the braking force line —
f
R ratio at the brake actuator pressure —
p
z braking rate —
z braking rate of laden motor vehicle —
M,lad
z braking rate of laden trailer vehicle —
R,lad
NOTE Subscript i indicates axles 1, 2, 3, . n, respectively.

2 © ISO 2008 – All rights reserved

Table 2 — Symbols specific to air over hydraulic (A/H) braking systems
Symbol Definition Unit
C conversion factor A/H converter front —
F
C conversion factor A/H converter rear —
R
p pneumatic pressure at front axle Pa
F
p hydraulic pressure at front axle Pa
HF
p hydraulic pressure at rear axle Pa
HR
p pneumatic pressure at rear axle Pa
R
p pressure attenuation ratio of load-conscious valve Pa/axle load
RATIO
NOTE All measurements are made with the vehicle stationary.
4 Test conditions and evaluations
4.1 General
The characteristics of roller brake testers shall be as specified in Annex A.
The efficiency test for braking systems shall be carried out with reference to the following:
⎯ legal requirements;
⎯ data provided by the vehicle manufacturer;
⎯ the instruction manual of the roller brake tester.
4.2 Preparation of vehicle and roller brake tester
4.2.1 Rollers and tyres shall be clean.
4.2.2 Tyre pressure shall be adjusted in accordance with the vehicle manufacturer's recommendations.
4.2.3 Additional instrumentation may measure the static axle loading without the rollers running.
4.2.4 Braking testing, for the purposes of official vehicle inspection, is to be carried out on a roller brake
tester certified by the technical services. Vehicle data and the measured values shall be recorded in the
forward direction.
4.3 Calculation and evaluation of test data
4.3.1 Braking efficiency calculation
4.3.1.1 General
For air over hydraulic and hydraulic braking systems, one of the major problems is to caculate the braking
efficiency without using an external pressure transducer on the hydraulic brake system. There is an increased
risk of leakages when measuring hydraulic systems, caused by connecting measurement devices.
The braking test may be made in the fully laden state, or in a lightly laden condition at lower actuation
pressures, on the assumption that braking forces increase predictably with increasing pressure.
4.3.1.2 Provisions for air over hydraulic braking system
For the front axle, if the air over hydraulic (A/H) conversion factor (C ) supplying the hydraulic pressure is
F
easily calculated from the measured air pressure (p ), then
F
p =×pC (1)
HF F F
In this case, the calculation is similar to the other possible extrapolation methods. A prerequisite is a
pneumatic measuring gauge before the A/H converter.
For the rear axle, the calculation is similar, but the function of load sensing valves needs to be taken into
account.
The characteristic of the load sensing/conscious valve shall be given in a graph or table, giving the pressure
attenuation ratio against load input:
pp=×C×p (2)
HR R R RATIO
In this case, the axle load needs to be known or measured.
The calculated hydraulic pressures, p and p , can be used as p is used in Equations (5) and (6).
HR HF Ai
The actuator pressure and brake force shall be determined simultaneously and in real time.
Extrapolation of brake output forces may be used to predict the laden braking rate. This may be achieved by
following one of the following extrapolation methods:
⎯ a minimum of 30 % of the design brake actuator pressure shall be achieved by suitable loading, dead
weight of the axle or by load simulation, or
⎯ the distance between the measurement points (the first point at the beginning and the second at the
cut-off point) shall be as large as possible in order to ensure the correct gradient of the function of the
graph (pressure versus force).
NOTE If it is prescribed in the relevant national requirements, the rolling resistance can be treated accordingly.
A plan of an air over hydraulic braking system is given in Figure 1.
...