ISO 26867:2009

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 2009
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©  ISO 2009
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ii © ISO 2009 – All rights reserved

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
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

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.
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

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.
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:
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:
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:
vv−
be
d = (3)
mfd
25,92×−s s
()
eb
2 © ISO 2009 – All rights reserved

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.
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
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
I Test inertia reflected at the brake kg⋅m
4 © ISO 2009 – All rights reserved

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
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.
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.
6 © ISO 2009 – All rights reserved

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
...