Road vehicles -- Brake lining friction materials -- Friction behaviour assessment for automotive brake systems

ISO 26867:2009 describes a test procedure for assessing the influence of pressure, temperature, and linear speed on the coefficient of friction of a given friction material in combination with a specific mating component (rotor or drum). ISO 26867:2009 is intended for use when comparing friction materials under the same conditions, or when controlling friction behaviour against a specification or certain performance limits. In order to take into account the different types of dynamometer cooling systems and to ensure repeatable temperature increments, the brake temperature is the control item during the fade sections. The types of brakes and discs used will vary according to individual projects. Production verification testing can use the results from this test in conjunction with a statistical process control system as part of a quality assurance plan. The specific project or programme will detail the applicable limits and assessment criteria. ISO 26867:2009 also allows for additional sections and brake applications that can prove useful during product development testing.

Véhicules routiers -- Matériaux de friction pour garnitures de freins -- Évaluation du comportement au frottement pour les systèmes de freinage automobiles

General Information

Status
Published
Publication Date
05-Jul-2009
Current Stage
9093 - International Standard confirmed
Start Date
25-May-2020
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INTERNATIONAL ISO
STANDARD 26867
First edition
2009-07-01
Road vehicles — Brake lining friction
materials — Friction behaviour
assessment for automotive brake
systems
Véhicules routiers — Matériaux de friction pour garnitures de freins —
Évaluation du comportement au frottement pour les systèmes de
freinage automobiles
Reference number
ISO 26867:2009(E)
ISO 2009
---------------------- Page: 1 ----------------------
ISO 26867:2009(E)
PDF disclaimer

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shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In

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accepts no liability in this area.
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the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.

COPYRIGHT PROTECTED DOCUMENT
© ISO 2009

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
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Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
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Web www.iso.org
Published in Switzerland
ii © ISO 2009 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 26867:2009(E)
Contents Page

Foreword............................................................................................................................................................. v

Introduction ....................................................................................................................................................... vi

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

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

3 Terms and definitions........................................................................................................................... 1

4 Symbols and abbreviated terms ......................................................................................................... 4

4.1 Symbols ................................................................................................................................................. 4

4.2 Abbreviated terms ................................................................................................................................ 6

5 Test conditions and preparation ......................................................................................................... 6

5.1 Inertia for the front axle........................................................................................................................ 6

5.2 Inertia for the rear axle ......................................................................................................................... 6

5.3 Test wheel load ..................................................................................................................................... 6

5.4 Pressure ramp rate ............................................................................................................................... 6

5.5 Maximum pressure ............................................................................................................................... 6

5.6 Pressure level with no power assist................................................................................................... 7

5.7 Sampling rate ........................................................................................................................................ 7

5.8 Initial brake temperature ...................................................................................................................... 7

5.9 Brake warm-up...................................................................................................................................... 7

5.10 Temperature measurement.................................................................................................................. 7

5.11 Brake fluid displacement measurement............................................................................................. 7

5.12 Cooling air conditions.......................................................................................................................... 7

5.13 Cooling air velocity or volume ............................................................................................................ 7

5.14 Conditioning settings for temperature and absolute humidity (humidity ratio) ............................ 7

5.15 Dynamometer rotational speed between brake applications........................................................... 8

5.16 Orientation of brake set-up.................................................................................................................. 8

5.17 Direction of air concerning brake set-up ........................................................................................... 8

5.18 Brake cooling rate................................................................................................................................. 8

5.19 Wear measurement............................................................................................................................... 8

5.20 Lateral run-out....................................................................................................................................... 8

5.21 Rotor or drum condition....................................................................................................................... 8

5.22 Fade sections ........................................................................................................................................ 8

5.23 Data collection ...................................................................................................................................... 9

6 Test procedures .................................................................................................................................. 10

6.1 Test procedure for product monitoring with no optional brake applications .............................. 10

6.2 Test procedure for product development with additional brake applications ............................. 12

6.3 Standard friction values calculated during test procedure............................................................ 14

7 Test report ........................................................................................................................................... 15

7.1 General................................................................................................................................................. 15

7.2 Graphical report.................................................................................................................................. 15

7.3 Tabular data for each brake application........................................................................................... 15

7.4 Wear measurements........................................................................................................................... 15

7.5 Test conditions ................................................................................................................................... 15

7.6 Cooling air conditions........................................................................................................................ 15

7.7 Brake cooling rate............................................................................................................................... 16

7.8 Friction values..................................................................................................................................... 16

7.9 Statistical analysis.............................................................................................................................. 16

Annex A (informative) Sample report for disc brakes .................................................................................. 17

© ISO 2009 – All rights reserved iii
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ISO 26867:2009(E)

Annex B (informative) Histograms for instantaneous friction values......................................................... 20

Annex C (informative) Reference calculations for cooling air speed and flow.......................................... 22

Bibliography ..................................................................................................................................................... 24

iv © ISO 2009 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 26867:2009(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 26867 was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 2, Braking

systems and equipment.
© ISO 2009 – All rights reserved v
---------------------- Page: 5 ----------------------
ISO 26867:2009(E)
Introduction

In the process of harmonizing automotive brake system applications, the modernization of friction behaviour

characterization is a top priority. This International Standard is intended to replace previous friction evaluation

test procedures based solely on drag brake applications, which do not take into account real-life driving

conditions or vehicle specific parameters.

The varied conditions under which the friction material is evaluated ensures a wide spectrum of data, which is

critical during the various phases of product life, such as product and manufacturing process development,

production validation, quality control, product auditing and field issues evaluation.

This International Standard is intended to be used in conjunction with other applicable standards or test

procedures (ISO, SAE, JIS/JASO, Federal Codes or Regulations, and other project or company-specific

testing programmes) to fully assess the adequacy of a friction material for use in a certain application, market

or vehicle platform. This International Standard does not include performance requirements related to

stopping distance or braking force distribution, under different vehicle conditions of speed, temperature, tyre-

to-road adhesion, loads and operating conditions of the braking system, as indicated in Federal Codes or

Regulations.

This International Standard is intended as a friction evaluation inertia-dynamometer test procedure to replace

previous test protocols that depend solely upon drag applications. This International Standard supports the

friction assessment during the life cycle of a friction material.

Friction evaluation and characterization by performing drag applications, which were once a valid replacement

for sample and scale testing, have now proven a limited approach. Drag applications do not correlate with

real-world driving conditions, brake system characteristics or vehicle dynamics. The chemistry and structure of

the transfer layers developed at the surface of the friction couple (friction lining and mating rotor or drum) and

the resulting coefficient of friction varies as a function of changing characteristics, e.g. sliding speed, surface

and bulk temperatures, braking pressure, braking energy and surface topology. During any given brake

application, the braking energy varies as a result of the mass distribution and dynamic mass transfer on the

vehicle. This is directly related to the vehicle's wheelbase, centre of gravity and vehicle height, which in itself

can directly influence the friction material behaviour. The same brake lining or part number, when used on

different vehicles, can perform differently depending upon its load, velocity, operating temperature, application

force and work history. Modern testing equipment enables friction formulators, process designers, applications

engineers and manufacturing personnel to obtain a wide and detailed characterization on the different levels

of friction witnessed by the brake lining or pad during various brake conditions.

This International Standard is designed to evaluate the friction behaviour under a wide array of driving speeds,

brake temperatures, brake pressure and deceleration levels. This new procedure provides the following

benefits:

⎯ a standard method for determining friction characteristics during early screening, benchmarking;

development or production monitoring;
⎯ the use of average by distance torque and pressure calculations;
⎯ instantaneous friction statistics;
⎯ an estimation of stopping distance using mean fully developed deceleration;
⎯ controlled and recorded environmental conditions.
vi © ISO 2009 – All rights reserved
---------------------- Page: 6 ----------------------
INTERNATIONAL STANDARD ISO 26867:2009(E)
Road vehicles — Brake lining friction materials — Friction
behaviour assessment for automotive brake systems
1 Scope

This International Standard describes a test procedure for assessing the influence of pressure, temperature,

and linear speed on the coefficient of friction of a given friction material in combination with a specific mating

component (rotor or drum).

This International Standard is intended for use when comparing friction materials under the same conditions,

or when controlling friction behaviour against a specification or certain performance limits. In order to take into

account the different types of dynamometer cooling systems and to ensure repeatable temperature

increments, the brake temperature is the control item during the fade sections. The types of brakes and discs

used will vary according to individual projects.

Production verification testing can use the results from this test in conjunction with a statistical process control

system as part of a quality assurance plan. The specific project or programme will detail the applicable limits

and assessment criteria.

This International Standard also allows for additional sections and brake applications that can prove useful

during product development testing.
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.

ISO 611, Road vehicles — Braking of automotive vehicles and their trailers — Vocabulary

ISO 15484, Road vehicles — Brake lining friction materials — Product definition and quality assurance

UNECE Regulation No.13-H, Uniform provisions concerning the approval of passenger cars with regard to

braking
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 611, ISO 15484,

UNECE Regulation No.13-H and the following apply.
3.1
friction value

average by distance of all instantaneous friction values for disc brakes or for drum brakes after the brake

reaches 95 % of the set point value (pressure or deceleration) until it falls below 95 % of the set point level

NOTE 1 For disc brakes, the friction value is obtained using Equation (1) (see definition 3.2).

NOTE 2 For drum brakes, the friction value is obtained using Equation (2) (see definition 3.3).

NOTE 3 The average by distance friction value from each individual brake application is the value referenced as

“friction value” in Table 4.
© ISO 2009 – All rights reserved 1
---------------------- Page: 7 ----------------------
ISO 26867:2009(E)
3.2
instantaneous friction value

〈disc brake〉 ratio of instantaneous output torque to instantaneous input torque at any specific point in time,

calculated as follows:
10 × M
d,brake
µ* = (1)
2×−pp ×A×r ×η
threshold p eff
where
M is the measured torque;
d,brake
p is the applied pressure;

p is the threshold pressure or minimum pressure required to develop braking torque;

threshold
A is the piston area;
r is the brake effective radius;
eff
η is the efficiency
3.3
instantaneous effectiveness value

〈drum brake〉 ratio instantaneous output torque to instantaneous input torque at any specific point in time,

calculated as follows:
10 × M
d,brake
C* = (2)
pp−×A×r×η
threshold p eff
where
M is the measured torque;
d,brake
p is the applied pressure;

p is the threshold pressure or minimum pressure required to develop braking torque;

threshold
A is the piston area;
r is the brake effective radius;
eff
η is the efficiency
3.4
mean fully developed deceleration
mfd
deceleration calculated as follows:
vv−
d = (3)
mfd
25,92×−s s
2 © ISO 2009 – All rights reserved
---------------------- Page: 8 ----------------------
ISO 26867:2009(E)
where
v is the release speed;
v is the linear speed at 0,8v ;
b p
v is the prescribed or braking speed for the brake application;
s is the calculated distance travelled between v and v ;
e p e
s is the calculated distance travelled between v and v
b p b

NOTE Equation (3) applies only when the release speed v is lower than 0,5v . The d calculation for brake

e p mfd

applications with v higher than 0,5v provides a very short range of data to perform a useful calculation. For certain brake

e p
applications, 0,8v can be lower than the release speed.
3.5
step

sequence number to label the different sections (3.6) during the test and ensure the test is conducted in the

prescribed order
3.6
section

group of similar brake applications under similar conditions or following a specific logic

NOTE 1 The brake applications can be stops (3.7) or snubs (3.8).

NOTE 2 The specific logic can be increasing brake pressure, increasing initial speed, or increasing brake temperature.

3.7
stop
brake stop

brake application where the brake slows down the test inertia until the equivalent linear speed is 0,5 km/h or

less
3.8
snub
brake snub

brake application where the brake slows down the test inertia to an equivalent linear speed above 5 km/h

3.9
characteristic section

series of brake snubs (3.8) at moderate speed, brake pressure and temperature, in order to assess how the

friction level changes as the test progresses

NOTE This involves green or new characteristic, stability checks after each burnish cycle, and immediately before or

after low speed/low pressure sections (3.6).
3.10
burnish section

series of brake snubs (3.8) at varying braking power in order to condition the friction couple and develop a

steady coefficient of friction

NOTE Varying braking power involves changing deceleration at constant kinetic energy dissipation.

3.11
ramp application section

series of brake stops (3.7) where the brake pressure increases steadily and slowly, in order to assess the

friction change with increasing input force
NOTE This is especially useful for drum brake systems.
© ISO 2009 – All rights reserved 3
---------------------- Page: 9 ----------------------
ISO 26867:2009(E)
3.12
low speed/low pressure section
series of brake stops (3.7) at low energy and low brake pressure
EXAMPLE In stop-and-go traffic or low speed manoeuvring.
3.13
pressure line section

series of brake snubs (3.8) at moderate energy in order to assess the effect on friction level as a function of

increasing input brake pressure
3.14
speed line section

series of brake snubs (3.8) at constant input brake pressure and increasing speeds, and hence kinetic

energy
3.15
failed booster section

series of brake stops (3.7) in order to assess the torque output while simulating a failed condition when the

vacuum or hydraulic assist unit is fully depleted, and when only the driver input load at the brake pedal, brake

pedal amplification and master cylinder multiplication factors are used to generate input pressure to the brake

corner
3.16
motorway applications section

series of brake snubs (3.8) in order to assess the ability of the brake to develop torque at or near highway

speeds
3.17
fade section

series of brake stops (3.7) intended to heat the brake and assess the coefficient of friction sensitivity to the

increasing elevated temperatures on the surface of the mating couple
3.18
hot performance section

series of brake snubs (3.8) similar to the pressure line but at elevated temperatures, in order to simulate

heavy braking or overloaded conditions
4 Symbols and abbreviated terms
4.1 Symbols
Symbol Definition Unit
A Total piston area mm
C* Instantaneous effectiveness value for drum brakes —
a 2
d Mean fully developed deceleration when v > 0,5v m/s
mfd e p
F Test wheel load N
F Test wheel load for front brakes at m N
f,dyn GV
F Test wheel load for rear brakes at m N
r,dyn GV
F Static axle load on the rear axle at m N
r,static GV
H Centre of gravity height m
I Test inertia reflected at the brake kg⋅m
4 © ISO 2009 – All rights reserved
---------------------- Page: 10 ----------------------
ISO 26867:2009(E)
L Vehicle wheel base m
m Gross vehicle mass kg
M Brake torque at 1,0 g deceleration N⋅m
M Measured torque N⋅m
d,brake
N Brake application number during the fade section —
p Applied pressure kPa
p Maximum hydraulic pressure kPa
max
p Threshold pressure or minimum pressure required to develop braking torque kPa
threshold
p Pressure at 500 N pedal force with no power assist for FMVSS 135 vehicles kPa
500,nopower
p Pressure at 667 N pedal force with no power assist for FMVSS 105 vehicles kPa
667,nopower
r Brake effective radius mm
eff
R Dynamic tyre effective rolling radius m
s Calculated distance travelled between v and v m
b p b
s Calculated distance travelled between v and v m
e p e
s Normalized stopping distance m
norm
T Maximum temperature for fade sections °C
max
T Starting temperature for the Nth brake application during the fade section °C
start,N

T Starting temperature for the first brake application during the fade section °C

start,1

T Starting temperature for the fifteenth brake application during the fade section °C

start,15
v Linear speed at 0,8v km/h
b p
v Linear speed at 0,1v for stops or release speed for brake snubs km/h
e p
v Vehicle maximum rated speed km/h
max
v Prescribed or braking speed for the brake application km/h
z Deceleration m/s
µ Average by distance friction value for disc brakes —
µ* Instantaneous friction value for disc brakes —
η Brake efficiency %
In accordance with UNECE Regulation No.13-H.
9,806 65 = 1 kgf. The use of the unit kgf is deprecated.
Using FMVSS 135 and UNECE Regulation No.13-H nominal values.
If different from nominal.
© ISO 2009 – All rights reserved 5
---------------------- Page: 11 ----------------------
ISO 26867:2009(E)
4.2 Abbreviated terms
ABS antilock braking system
DTV disc thickness variation
ESP electronic stability programme
FMVSS Federal Motor Vehicle Safety Standard
LRO lateral run-out
NVH noise, vibration and harshness
OE original equipment
UNECE United Nations Economic Commission for Europe
VSC vehicle stability control
5 Test conditions and preparation
5.1 Inertia for the front axle

The inertia for the front axle shall be calculated using 75 % of half the gross vehicle mass, unless otherwise

specified for the project and the tyre rolling radius.
5.2 Inertia for the rear axle

The inertia for the rear axle shall be calculated using 25 % of half the gross vehicle mass, unless otherwise

specified for the project and the tyre rolling radius.
5.3 Test wheel load

When vehicle parameters are available for the project, the test wheel load can also be calculated according to

Equation (4) for front brakes or Equation (5) for rear brakes. Wheel load shall take into account static loading

and dynamic mass transfer at a vehicle deceleration of 0,3 g.
⎛⎞ m
r,static
Fz=−1 + × (4)
f,dyn
mL 2
⎝⎠GV
⎛⎞F
r,static
Fz=−1 − × (5)
r,dyn
mL 2
5.4 Pressure ramp rate

The pressure ramp rate shall be (25 000 ± 5 000) kPa/s for all brake applications.

5.5 Maximum pressure

The maximum pressure applied to the brake can be lower than that specified in this International Standard in

order to accommodate specific brake configurations or brake system design parameters.

6 © ISO 2009 – All rights reserved
---------------------- Page: 12 ----------------------
ISO 26867:2009(E)
5.6 Pressure level with no power assist

If vehicle-specific data is available, pressure shall be used that is equivalent to the maximum allowable pedal

force with the power assist unit fully depleted:

⎯ for vehicles certified under FMVSS 105, the maximum allowable pedal force is 667 N;

⎯ for vehicles certified under FMVSS 135, the maximum allowable pedal force is 500 N.

5.7 Sampling rate
The sampling rate shall be at least 100 Hz for pressure and torque.
5.8 Initial brake temperature

The initial brake temperature shall be the real-time temperature on the rotor or drum at the start of the brake

application.
5.9 Brake warm-up

When the rotor or drum temperature is below the initial temperature required for the brake application, the

brake shall be dragged at the braking speed of the intended brake event without exceeding 80 km/h at 2 m/s

equivalent torque for 20 s.

Alternatively, brake applications of the intended brake event shall be performed to raise the temperature.

5.10 Temperature measurement

One thermocouple shall be positioned at the centre of the friction path (0,5 ± 0,1) mm deep in the outer face of

the disc or drum contact face. The initial brake temperature shall be measured using the disc or drum

thermocouple. Additional thermocouple(s) can be set in the friction material for temperature recording

purposes.
5.11 Brake fluid displacement measurement

Fluid displacement of the brake during all brake application shall be recorded and reported at the end of the

test.
5.12 Cooling air conditions

For steps 13, 14 and 18 (see Tables 2 and 3), the cooling air speed shall be set to 1 m/s or the equivalent air

volume. If the dynamometer has exhaust cooling air capabilities, it shall be kept running during the entire test.

For all other sections, the cooling air speed may be adjusted depending upon the brake being tested or the

dynamometer being used, in order to maintain the efficiency of the test.
5.13 Cooling air velocity or volume

The cooling air velocity or volume shall be specified in m/s or m /h, as measured in the duct. The duct outlet

shall be nominally 300 mm to 400 mm away from the test hardware. For more details for determining the

approximate relationship between air volume, air speed, duct size and duct outlet distance to the brake, see

Annex C.

5.14 Conditioning settings for temperature and absolute humidity (humidity ratio)

The cooling air conditioning for temperature and absolute humidity shall be reported as the average of all

brake events taken at the start of the brake application. The nominal cooling air temperature is (20 ± 5) °C and

© ISO 2009 – All rights reserved 7
---------------------- Page: 13 ----------------------
ISO 26867:2009(E)

absolute humidity 7,29 g/kg (8,68 g/m ) measured at sea level. The appropriate psychrometric chart shall be

used to find operating limits at temperatures other than 20 °C, or elevations other than sea level.

NOTE Nominal cooling air conditions are equivalent to (20 ± 5) °C and (50 ± 10) % relative humidity.

5.15 Dynamometer rotational speed between brake applications

The dynamometer rotational speed during cooling between brake event shall be equal to 50 % of the braking

speed for the next brake application, except for steps 13, 14, and 18 (see Tables 2 and 3), where it can be

equal to the braking speed for the next brake application in order to minimize warm-up brake application

...

DRAFT INTERNATIONAL STANDARD ISO/DIS 26867
ISO/TC 22/SC 2 Secretariat: AFNOR
Voting begins on: Voting terminates on:
2008-02-22 2008-07-22

INTERNATIONAL ORGANIZATION FOR STANDARDIZATION • МЕЖДУНАРОДНАЯ ОРГАНИЗАЦИЯ ПО СТАНДАРТИЗАЦИИ • ORGANISATION INTERNATIONALE DE NORMALISATION

Road vehicles — Brake lining friction materials — Friction
behaviour assessment for automative brake systems

Véhicules routiers — Matériaux de friction pour garnitures de freins — Évaluation du comportement en friction

pour les systèmes de freinage automatiques
ICS 43.040.40

In accordance with the provisions of Council Resolution 15/1993 this document is circulated in

the English language only.

Conformément aux dispositions de la Résolution du Conseil 15/1993, ce document est distribué

en version anglaise seulement.

To expedite distribution, this document is circulated as received from the committee secretariat.

ISO Central Secretariat work of editing and text composition will be undertaken at publication

stage.

Pour accélérer la distribution, le présent document est distribué tel qu'il est parvenu du

secrétariat du comité. Le travail de rédaction et de composition de texte sera effectué au

Secrétariat central de l'ISO au stade de publication.

THIS DOCUMENT IS A DRAFT CIRCULATED FOR COMMENT AND APPROVAL. IT IS THEREFORE SUBJECT TO CHANGE AND MAY NOT BE

REFERRED TO AS AN INTERNATIONAL STANDARD UNTIL PUBLISHED AS SUCH.

IN ADDITION TO THEIR EVALUATION AS BEING ACCEPTABLE FOR INDUSTRIAL, TECHNOLOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT

INTERNATIONAL STANDARDS MAY ON OCCASION HAVE TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL TO BECOME STANDARDS TO

WHICH REFERENCE MAY BE MADE IN NATIONAL REGULATIONS.

RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT, WITH THEIR COMMENTS, NOTIFICATION OF ANY RELEVANT PATENT RIGHTS OF WHICH

THEY ARE AWARE AND TO PROVIDE SUPPORTING DOCUMENTATION.
International Organization for Standardization, 2008
---------------------- Page: 1 ----------------------
ISO/DIS 26867
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.

Copyright notice

This ISO document is a Draft International Standard and is copyright-protected by ISO. Except as permitted

under the applicable laws of the user's country, neither this ISO draft nor any extract from it may be

reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, photocopying,

recording or otherwise, without prior written permission being secured.

Requests for permission to reproduce should be addressed to 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
Reproduction may be subject to royalty payments or a licensing agreement.
Violators may be prosecuted.
ii ISO 2008 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/DIS 26867
Contents Page

1 Scope and field of application .............................................................................................................1

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

3 Symbols and abbreviated terms ..........................................................................................................1

4 Terms and definitions ...........................................................................................................................2

5 Test conditions and preparation..........................................................................................................5

5.1 Inertia for the front axle ........................................................................................................................5

5.2 Inertia for the rear axle..........................................................................................................................5

5.3 Test wheel load......................................................................................................................................5

5.4 Pressure ramp rate................................................................................................................................6

5.5 Maximum pressure................................................................................................................................6

5.6 Pressure level with no power assist....................................................................................................6

5.7 Sampling rate.........................................................................................................................................6

5.8 Initial brake temperature.......................................................................................................................6

5.9 Brake warm-up.......................................................................................................................................6

5.10 Temperature measurement ..................................................................................................................6

5.11 Brake fluid displacement measurement .............................................................................................6

5.12 Cooling air conditions...........................................................................................................................6

5.13 Cooling air velocity or volume .............................................................................................................7

5.14 Conditioning settings for temperature and absolute humidity (humidity ratio).............................7

5.15 Dynamometer rotational speed between brake applications ...........................................................7

5.16 Orientation of brake setup....................................................................................................................7

5.17 Direction of air with regard to brake setup.........................................................................................7

5.18 Brake cooling rate .................................................................................................................................7

5.19 Wear measurement ...............................................................................................................................7

5.20 Lateral run-out .......................................................................................................................................7

5.21 Rotor or drum conditions .....................................................................................................................7

5.22 Fade sections.........................................................................................................................................8

5.23 Data collection.......................................................................................................................................9

6 Test procedures.....................................................................................................................................9

6.1 Test procedure for product monitoring with no optional brake applications.................................9

6.2 Test procedure for product development with additional brake applications..............................10

7 Test report............................................................................................................................................12

7.1 Graphical report...................................................................................................................................12

7.2 Tabular data for each brake application ...........................................................................................12

7.3 Wear measurements ...........................................................................................................................13

7.4 Test conditions ....................................................................................................................................13

7.5 Cooling air conditions.........................................................................................................................13

7.6 Brake cooling rate ...............................................................................................................................13

7.7 Friction values .....................................................................................................................................13

7.8 Statistical analysis ..............................................................................................................................13

Annex A (informative) Vehicle and test parameters (per clause 5) .............................................................14

Annex B (informative) Sample report for disc brakes...................................................................................15

B.1 graphical summaries...........................................................................................................................15

B.1.1 constant deceleration or pressure sections, graph instantaneous values versus stop or snub

number...................................................................................................................................................15

B.1.2 Burnish section, graph snubs 2, 15, and 30. ......................................................................................15

B.1.3 Average by distance friction marker, include a marker for the average by distance friction for

all the stops or snubs graphed. .............................................................................................................15

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ISO/DIS 26867

Annex C (informative) Histograms for instantaneous friction values (per clauses 7.1.3 and 7.1.4) ....... 17

Annex D (informative) Reference calculations for cooling air speed and flow (per clause 5.13) ............ 19

D.1 Conversion between airflow and cooling air speed........................................................................ 19

D.2 Calculation of cooling air speed passing over the brake............................................................... 20

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ISO/DIS 26867
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 26867 was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 2, Brake

systems and equipment.
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ISO/DIS 26867
Introduction

The efforts of harmonization among different countries and technical groups have the modernization of friction

behaviour characterization of automotive brake systems applications as a top priority. This International

Standard is intended to replace previous friction evaluation testing based solely on drag brake applications,

which do not take into account real-life driving conditions, or vehicle specific parameters.

The varied condition under which the friction material is evaluated ensures a wide spectrum of data that is

critical during the various phases of product life such as product and manufacturing process development,

production validation, quality control, product auditing and field issues evaluation.

Use this International Standard in conjunction with other applicable standards or test procedures (ISO, SAE,

JASO, Federal Codes or regulations, and other project or company-specific testing programs) to fully assess a

friction material’s adequacy for use in a certain application, market or vehicle platform. This International

Standard does not include performance requirements related to stopping distance or braking force distribution,

under different vehicle conditions of speed, temperature, tire-to-road adhesion, loads, and operating

conditions of the braking system as indicated on Federal Codes or Regulations.

This International Standard is intended as a friction evaluation inertia-dynamometer test procedure to replace

previous test protocols that depend solely upon drag applications. This Standard supports the friction

assessment during the life cycle of a friction material.

Friction evaluation and characterization by performing drag applications, which were once a valid replacement

for sample and scale testing, have now proven a limited approach. Drag applications do not correlate with

real-world driving conditions, brake system characteristics, or vehicle dynamics. Lining transfer layer

properties, hence friction level is heavily dependant upon the type of brake application. During any given

brake application the braking energy varies as a result from the weight distribution and dynamic weight

transfer on the vehicle. This is directly related to the vehicle’s wheelbase, centre of gravity, and vehicle height,

which in itself can influence directly the friction material behaviour. The same brake lining or part number,

when used on different vehicles, can perform differently depending upon its load, velocity, operating

temperature, application force, and work history. Modern testing equipment provides friction formulators,

process designers, applications engineers, and manufacturing personnel the ability to obtain a wide and

detailed characterization on the different levels of friction witnessed by the brake lining or pad during various

brake conditions.

This International Standard is designed to evaluate the friction behaviour under a wide array of driving speeds,

brake temperatures, brake pressure, and deceleration levels. Some benefits of this new procedure are:

⎯ standard method to determining friction characteristics during early screening, benchmarking;

development or production monitoring;
⎯ use of average by distance torque and pressure calculations;
⎯ instantaneous friction statistics;
⎯ estimation of stopping distance using mean fully developed deceleration;
⎯ controlled and recorded environmental conditions.
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ISO/DIS 26867
Road vehicles — Brake lining friction materials — Friction
behaviour assessment for automative brake systems
1 Scope and field of application

This inertia-dynamometer standard describes the influence of pressure, temperature, and linear speed on the

coefficient of friction of a given friction material in combination with a specific mating component (rotor or

drum). Use this standard when you need to compare friction materials under the same conditions or to control

the friction behaviour against a specification or certain performance limits. To take into account the different

types of dynamometer cooling systems and ensure repeatable temperature increments, the brake temperature

is the control item during the fade sections. The types of brakes and discs used will vary according to

individual projects.

Production verification testing can use the results from this test in conjunction with a statistical process control

system as part of a quality assurance plan. The specific project or program will detail the applicable limits and

assessment criteria. This standard allows as well additional sections and brake applications very useful during

product development testing. The additional brake applications added for the development testing are

indicated in bold.
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.

ISO 15484— Road vehicles - Brake Linings – Friction Materials – Product definition and assurance

ISO 611:2003 Road vehicles - Braking of automotive vehicles and their trailers – Vocabulary

ECE Regulation 13-H Uniform Provisions Concerning the Approval of: Passenger Cars with Regard to

Braking.
3 Symbols and abbreviated terms
Symbol Unit Description
α m/s² Deceleration
A mm Piston area
C* - instantaneous effectiveness value for drum brakes
GVW kgf Gross vehicle weight
H m Centre of gravity height
I kg·m Inertia reflected at the brake
1) To be published.
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ISO/DIS 26867
Symbol Unit Description
L m Vehicle wheel base
LRO µm Lateral Ron-out
Md N·m Brake torque at 1.0 g
Md N·m Measured torque
Brake

mfdd m/s Mean fully developed deceleration when release speed > 0.5· v per ECE Reg. 13-H

N - Snub number during the fade section
P kPa Applied pressure
p kPa Maximum hydraulic pressure
max
p kPa Threshold pressure or minimum pressure required to develop braking torque
Threshold
P kPa Pressure at 500 N pedal force with no power assist for FMVSS 135 vehicles
500no-p

667no-p kPa Pressure at 667 N pedal force with no power assist for FMVSS 105 vehicles

r mm Brake effective radius
eff
R m Dynamic tire effective rolling radius
s m Calculated distance travelled between v and v
b p b
s m Calculated distance travelled between v and v
e p e
S m Normalized stopping distance using FMVSS 135 and ECE Regulation 13-H nominal
norm
values
T C Initial brake temperature for snub number N during the fade section
T C Initial brake temperature for snub number 1 during the fade section
T C Initial brake temperature for snub number 15 during the fade section
A15
T C Maximum temperature for fade sections
max
v km/h
Linear speed at 0.8⋅v
b p
v km/h
e Linear speed at 0.1⋅v for stops or release speed for brake snubs
km/h Vehicle maximum rated speed
max
km/h Prescribed or braking speed for the brake application
kgf Test wheel load
kgf Static axle load on the rear axle at GVW
r-static
µ* - Instantaneous friction value for disc brakes
µ - Average by distance friction value for disc brakes
η Efficiency taken as 1
4 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 15484, ECE Regulation 13-H, ISO

611:2003 and the following apply.
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ISO/DIS 26867
4.1
friction value

average by distance of all instantaneous friction values obtained using equation1 for disc brakes or equation 2

for drum brakes after the brake reaches 95% of the set point value (pressure or deceleration) until it falls

below 95% of the set point level

NOTE This average by distance friction value from each individual brake application is the value referenced as

“friction value” for definitions 4.4 through 4.25.
4.2
instantaneous friction value

ratio of instantaneous output torque to instantaneous input torque for a disc brake at any specific point in time

according to Equation 1
10 × Md
Brake
µ*=
2×()p− p × A × r ×η
Threshold P eff
(1)
4.3
C* value

Ratio of instantaneous output torque to instantaneous input torque for a drum brake at any specific point in

time according to Equation 2
10 × Md
Brake
C*=
(2)
p− p × A × r ×η
Threshold P eff
4.4
test average µ value

average friction value from all brake applications from steps 3, 5 (last 5 stops), 7, 8, 12, 16, 17, and 20 without

optional brake applications
4.5
test minimum µ value

lowest friction values from steps 3, 5 (last 5 stops), 7, 8, 12, 16, 17, and 20 without including optional brake

applications
4.6
test maximum µ value

highest friction values from steps 3, 5 (last 5 stops), 7, 8, 12, 16, 17, and 20 without including optional brake

applications
4.7
characteristic/stability check µ value
average and minimum friction values from last 3 brake applications from step 3
4.8
ramp applications µ value
average and minimum friction values from the two brake applications from step 4
4.9
cold characteristic µ value
friction value from first brake application from step 5
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ISO/DIS 26867
4.10
stability during cold characteristic µ values
average and minimum friction values from last 3 brake applications from step 5
4.11
low speed/low pressure (1) µ values
average and minimum friction values from all brake applications from step 6
4.12
pressure line (1) µ value at 6000 kPa
friction values from brake application at 6000 kPa from step 7
4.13
high speed µ value

friction values from last brake application from step 8 without including optional brake applications

4.14
normalized stopping distance during FMVSS 135 failed booster
normalized stopping distance from stops 1 and 6 from step 9
4.15
0,9v motorway µ value
max
friction value from last brake application from step 10
4.16
low speed/low pressure (2) µ values
average and minimum friction values from all brake applications from step 11
4.17
characteristic/recovery (1) µ values
average and minimum friction values from last 3 brake applications from step 12
4.18
fade 1 minimum µ value
minimum friction value from step 13
4.19
hot performance µ value
minimum friction value from last 5 brake applications from step 14
4.20
low speed/low pressure (3) µ values
average and minimum friction values from all brake applications from step 15
4.21
characteristic/recovery (2) µ values
average and minimum friction values from last 3 brake applications from step 16
4.22
pressure line (2) µ value at 6000 kPa
friction values from brake application at 6,000 kPa from step 17
4.23
fade 2 minimum µ value
minimum friction value from step 18
4.24
low speed/low pressure (4) µ values
average and minimum friction values from all brake applications from step 19
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ISO/DIS 26867
4.25
final characteristic µ values
average and minimum friction values from last 3 brake applications from step 20
4.26
mfdd — mean fully developed deceleration
use equation 3.
v − v
b e
mfdd= (3)
25,92×()s − s
e b

equation 3 applies only when the release speed v is lower than 0,5×v . the mfdd calculation for brake

e p

applications with v higher than 0,5×v provides a very short range of data to perform a useful calculation. for

e p
certain brake applications 0,8×v can be lower than the release speed.
4.27
s — normalized stopping distance per FMVSS 135
norm

optional calculation to report results from the failed booster section. As an alternate method to estimate

stopping distance ability using the brake torque output from the friction material tested, use equation 4. This

equation is normalized for the allowable reaction and pressure build-up time based on best driver effort, and a

test speed from 100 km/h to 0 km/h from the federal code FMVSS 135.
386,7
S =10+
(4)
norm
mfdd
5 Test conditions and preparation
5.1 Inertia for the front axle

Calculate using 75% of half the gross vehicle weight unless otherwise specified for the project and the tire

rolling radius.
5.2 Inertia for the rear axle

Calculate using 25% of half the gross vehicle weight unless otherwise specified for the project and the tire

rolling radius.
5.3 Test wheel load

When vehicle parameters are available for the project, the test wheel load can also be calculated according to

Equation 5 for front brakes or Equation 6 for rear brakes. Wheel load shall take into account static loading and

dynamic weight transfer at a vehicle deceleration of 0.3 g.
⎛ ⎞
W h GVW
r−static
⎜ ⎟
W = 1− + ×α
(5)
f -dyn
⎜ ⎟
GVW L 2
⎝ ⎠
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ISO/DIS 26867
⎛ ⎞
W h GVW
r−static
⎜ ⎟
W = 1− − ×α
r-dyn
⎜ ⎟
GVW L 2
⎝ ⎠
(6)
5.4 Pressure ramp rate

The pressure ramp rate shall be 25.000 kPa/s + 5.000 kPa/s for all brake applications.

5.5 Maximum pressure

The maximum pressure applied to the brake may be lower than the ones specified on this International

Standard in order to accommodate specific brake configurations or brake system design parameters.

5.6 Pressure level with no power assist

If vehicle-specific data is available, use the pressure equivalent to the maximum allowable pedal force with the

power assist unit fully depleted.

NOTE Use 667 N of pedal force for vehicles certified under FMVSS 105 and 500 N of pedal force for vehicles

certified under FMVSS 135.
5.7 Sampling rate
The sampling rate shall be equal or more than100 Hz for pressure and torque.
5.8 Initial brake temperature

It shall be the real-time temperature on the rotor or drum at the start of the brake application.

5.9 Brake warm-up

When the rotor or drum temperature is below the initial temperature required for the brake application drag the

brake at the braking speed of the intended brake event without exceeding 80 km/h at 0,2 g equivalent torque

for 20 seconds.
5.10 Temperature measurement

Position one thermocouple at the centre of the friction path 0,5 mm + 0,1 mm deep in the outer face of the disc

or drum contact face and measure the Initial brake temperature using the disc or drum thermocouple.

Additional thermocouple(s) may be set in the friction material for temperature recording purposes.

5.11 Brake fluid displacement measurement

Fluid displacement of the brake during all brake application shall be recorded and reported at the end of the

test.
5.12 Cooling air conditions

For steps, 13, 14 and 18 cooling air speed shall be set to 1 m/s or the equivalent air volume. If the

dynamometer has exhaust cooling air capabilities keep it running during the entire test. For all other sections,

cooling air speed may be adjusted according to the brake being tested or the dynamometer being used to

keep the efficiency of the test.
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ISO/DIS 26867
5.13 Cooling air velocity or volume

It shall be specified in [m/s] or [m /h] as measured in the duct. Duct outlet shall be nominally 300mm to 400

mm away from the test hardware. For more details for determining the approximate relationship among air

volume, air speed, duct size, and duct outlet distance to the brake please refer to Annex E.

5.14 Conditioning settings for temperature and absolute humidity (humidity ratio)

Cooling air conditioning for temperature and absolute humidity as the average from all brake events taken at

the start of the brake application shall be reported. Nominal cooling air temperature is 20°C ± 5 C and

absolute humidity 7,29 g/kg (8,68 g/m ) measured at sea level. Use the appropriate psychrometric chart to find

operating limits at temperatures other than 20 C or elevations other than sea level.

NOTE Nominal cooling air conditions are equivalent to 20°C ± 5 C and (50 ± 10) % relative humidity.

5.15 Dynamometer rotational speed between brake applications

The dynamometer rotational speed during cooling between brake event equals 50% of the braking speed for

the next brake application, except for steps 13, 14, and 18 where it can be equal to the braking speed for the

next brake application to minimize warm-up brake applications.
NOTE Alternatevely 10 km/h is applicable for European programs.
5.16 Orientation of brake setup

Mount the fixture as close as possible to the vehicle position. In general, this helps correlation with issues like

brake drag, off-brake wea
...

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