ISO 26867:2009
(Main)Road vehicles — Brake lining friction materials — Friction behaviour assessment for automotive brake systems
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
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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
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ISO 26867:2009(E)
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accepts no liability in this area.
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© ISO 2009
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ii © ISO 2009 – All rights reserved
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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
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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
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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.
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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
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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
µ
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.
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ISO 26867:2009(E)
3.2
instantaneous friction value
µ*
〈disc brake〉 ratio of instantaneous output torque to instantaneous input torque at any specific point in time,
calculated as follows:
5
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;
p
r is the brake effective radius;
eff
η is the efficiency
3.3
instantaneous effectiveness value
C*
〈drum brake〉 ratio instantaneous output torque to instantaneous input torque at any specific point in time,
calculated as follows:
5
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;
p
r is the brake effective radius;
eff
η is the efficiency
3.4
mean fully developed deceleration
d
mfd
deceleration calculated as follows:
22
vv−
be
d = (3)
mfd
25,92×−s s
()
eb
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ISO 26867:2009(E)
where
v is the release speed;
e
v is the linear speed at 0,8v ;
b p
v is the prescribed or braking speed for the brake application;
p
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.
p
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.
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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
2
A Total piston area mm
p
C* Instantaneous effectiveness value for drum brakes —
a 2
d Mean fully developed deceleration when v > 0,5v m/s
mfd e p
b
F Test wheel load N
b
F Test wheel load for front brakes at m N
f,dyn GV
b
F Test wheel load for rear brakes at m N
r,dyn GV
b
F Static axle load on the rear axle at m N
r,static GV
H Centre of gravity height m
2
I Test inertia reflected at the brake kg⋅m
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ISO 26867:2009(E)
L Vehicle wheel base m
m Gross vehicle mass kg
GV
M Brake torque at 1,0 g deceleration N⋅m
d
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
c
s Normalized stopping distance m
norm
d
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
p
2
z Deceleration m/s
µ Average by distance friction value for disc brakes —
µ* Instantaneous friction value for disc brakes —
η Brake efficiency %
a
In accordance with UNECE Regulation No.13-H.
b
9,806 65 = 1 kgf. The use of the unit kgf is deprecated.
c
Using FMVSS 135 and UNECE Regulation No.13-H nominal values.
d
If different from nominal.
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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.
F
⎛⎞ m
H
r,static
GV
Fz=−1 + × (4)
⎜⎟
f,dyn
mL 2
⎝⎠GV
⎛⎞F
m
H
r,static
GV
Fz=−1 − × (5)
⎜⎟
r,dyn
mL 2
GV
⎝⎠
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.
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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
2
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
3
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
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ISO 26867:2009(E)
3
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
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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
iv © ISO 2008 – All rights reserved
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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.
1)
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
2
A mm Piston area
p
C* - instantaneous effectiveness value for drum brakes
GVW kgf Gross vehicle weight
H m Centre of gravity height
2
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
2
mfdd m/s Mean fully developed deceleration when release speed > 0.5· v per ECE Reg. 13-H
p
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
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
o
T C Initial brake temperature for snub number N during the fade section
AN
o
T C Initial brake temperature for snub number 1 during the fade section
A1
o
T C Initial brake temperature for snub number 15 during the fade section
A15
o
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
p
km/h Vehicle maximum rated speed
v
max
km/h Prescribed or braking speed for the brake application
v
p
kgf Test wheel load
W
kgf Static axle load on the rear axle at GVW
W
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
µ
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
µ*
ratio of instantaneous output torque to instantaneous input torque for a disc brake at any specific point in time
according to Equation 1
5
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
5
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.
2
2
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.
p
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
3
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
o
the start of the brake application shall be reported. Nominal cooling air temperature is 20°C ± 5 C and
3
absolute humidity 7,29 g/kg (8,68 g/m ) measured at sea level. Use the appropriate psychrometric chart to find
o
operating limits at temperatures other than 20 C or elevations other than sea level.
o
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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