ISO/PAS 22596:2022

PUBLICLY ISO/PAS
AVAILABLE 22596
SPECIFICATION
First edition
2022-05
Road vehicles — Brake lining friction
materials — Dynamometer metal
pick-up generation procedure for disc
brakes
Véhicules routiers — Matériaux de friction des garnitures de freins —
Procédure de génération de métal aggloméré sur freins à disque par
dynamomètre
Reference number
ISO/PAS 22596:2022(E)
© ISO 2022

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ISO/PAS 22596:2022(E)
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© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Published in Switzerland
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ISO/PAS 22596:2022(E)
Contents Page
Foreword .v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms.3
4.1 Symbols . 3
4.2 Abbreviated terms . 3
5 Test conditions and test preparation . .3
5.1 Inertia for the brake testing . 3
5.2 Pressure ramp rate . 4
5.3 Maximum pressure . 4
5.4 Sampling rate . 4
5.5 Initial brake temperature . 4
5.6 Brake temperature measurement . 4
5.7 Cooling air conditioning . 4
5.8 Cooling air velocity or volume . 4
5.9 Exhaust conditions . 4
5.10 Conditioning settings for temperature and absolute humidity (humidity ratio) . 4
5.11 Dynamometer rotational speed between brake applications . 5
5.12 Orientation of brake set-up . 5
5.13 Direction of air relative to the brake set-up . 6
5.14 Wear measurement . 6
5.15 Disc lateral run-out . 6
5.16 Caliper, disc or drum and pads condition . 6
5.17 Hot brake applications . 6
5.18 Water specification . 6
5.19 Specification of nozzles for water spraying . 6
5.20 Saltwater specification . 6
5.20.1 Recommended solution . 6
5.20.2 Alternative solutions . 7
5.20.3 Other solutions . 7
5.21 Noise and vibration (NVH) measurements . 7
5.22 Data collection . 7
6 Test procedures . 8
6.1 Basic information . 8
6.2 Test procedure: “heat and pressure MPU” . 8
6.3 Test procedures “water and saltwater MPU” . 9
6.3.1 Procedure 1 (core or early development testing) . 9
6.3.2 Procedure 2 (DVP procedure; can also be used in vehicle testing) . 10
6.4 Test procedure for “low load and pressure” . 14
7 Test report .15
7.1 General . 15
7.2 Test conditions . 15
7.2.1 Disc and lining identification . 15
7.2.2 Disc surface characterisation . 15
7.2.3 Photographs of the setup . 15
7.2.4 Photographs of the test parts . 15
7.2.5 Documentation of pad MPU number and area . 16
7.2.6 Documentation of disc surface profile . 17
7.2.7 Acceptance criteria . 19
7.3 Graphical report . 20
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ISO/PAS 22596:2022(E)
7.4 Cooling air conditions and water spraying . 20
7.5 Tabular data for each brake application . 20
7.6 Wear measurement; pad and disc appearance . 21
Annex A (informative) MPU shapes.22
Annex B (informative) Template proposal .24
Annex C (informative) Reference calculation for cooling air speed and flow .33
Annex D (informative) Specification of salt for “water and salt MPU” .35
Bibliography .36
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ISO/PAS 22596:2022(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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
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. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 33,
Vehicle dynamics and chassis components.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
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ISO/PAS 22596:2022(E)
Introduction
Metal pick-up (MPU) is a phenomenon/issue observed in automotive disc brakes during the braking
process. Worn metallic particles may agglomerate under specific conditions and embed in the friction
material. It may deteriorate brakes' appearance by scoring (grooves) on the surface of brake discs. MPU
is also suspected to be a root cause of brakes NVH (noise, vibrations and harshness) issues as brake
squeal or wire brush.
There is no single mechanism for creation of MPU in the automotive brakes so it cannot be only one
specific condition for testing it. While the so-called NAO (non-asbestos-organic) friction materials
are sensitive to high temperature and pressures, low metallic materials may create MPU under wet
conditions or even more under the saltwater influence.
This document describes and covers all known critical conditions for generating MPU, it specifies
which conditions are critical for a given friction material type. The methods described apply not only
in the development of the material composition, but also in the selection of the materials for new brake
applications and optimization of components for a recognised MPU issue.
This document includes three test procedures:
1. MPU generation under water/saltwater influence (typical for low metallic friction materials);
2. MPU generation at low temperatures and low brake pressures (typical for low metallic friction
materials);
3. MPU generation at high brake temperatures and brake pressures (typical for NAO friction
materials).
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PUBLICLY AVAILABLE SPECIFICATION ISO/PAS 22596:2022(E)
Road vehicles — Brake lining friction materials —
Dynamometer metal pick-up generation procedure for disc
brakes
1 Scope
This document describes test procedures for assessing the influence of pressure, temperature and
water/salt water on the generation of metal pick-up (MPU) for a given friction material in combination
with a specific brake disc. There are multiple tests to investigate the MPU generation issue for different
types of friction materials (so called NAO and low metallic materials) under critical environmental and
working conditions: influence of water and salt water, high temperatures and high pressures and low
temperatures and low pressures.
This document supports the friction material development process and selection of friction materials
for new brake applications.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 21920-2, Geometrical product specifications (GPS) — Surface texture: Profile — Part 2: Terms,
definitions and surface texture parameters
ISO 15484, Road vehicles — Brake lining friction materials — Product definition and quality assurance
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 611, ISO 15484 and the
following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
MPU
metal pick-up
disc material agglomeration or compaction of high hardness on or in the pad material surface
Note 1 to entry: The MPU shapes could be different (flakes, grains with different aspect ratio, colloquially called
“fishes”) and have different sizes (up to several millimetres).
3.2
groove
mechanical disc surface defect in the circumferential direction caused by metal pick-up (MPU) (3.1)
collected in the pad material with a depth of more than several tens of micrometres
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ISO/PAS 22596:2022(E)
3.3
friction value
µ
average by time of all instantaneous friction values (3.4)
Note 1 to entry: See Formula (1) for calculation and evaluate after the brake application reaches 95 % of the set
point value (pressure or deceleration) until it falls below 95 % of the set point level.
3.4
instantaneous friction value
µ*
ratio of instantaneous output torque to instantaneous input pressure at any specific point in time
Note 1 to entry: For calculation, see also Formula (1).
3.5
step
sequence number of labelling the different sections (3.6) during the test
Note 1 to entry: 1to entry: Sequence number ensures the test conduction in the prescribed order.
3.6
section
group of similar brake applications under similar conditions or following a specific logic
Note 1 to entry: The brake applications can be stopped.
Note 2 to entry: The specific logic can be increasing brake pressure, increasing initial speed, or increasing brake
temperature.
3.7
brake stop
brake application where the brake slows down the test inertia until the equivalent linear speed is
0,5 km/h
Note 1 to entry: Project dependent the final speed can be increased to 5 km/h max.
3.8
brake snub
brake application where the brake slows down the test inertia to an equivalent linear speed above
5 km/h
3.9
burnish section
series of brake stops (3.7) or brake snubs (3.8) to condition the friction couple by developing a steady
coefficient of friction and create friction film and brake dust between the brake pads and disc
3.10
water and salt water section
series of brake snubs (3.8) while water or salt water is added between pads and disc surface
Note 1 to entry: Water sections are used to create metal pick-up (MPU) (3.1) and evaluate friction level under wet
conditions.
3.11
heat and pressure section
section (3.6) of test procedure with a series of brake snubs (3.8) at elevated initial brake disc
temperatures (above 300 °C) and increased brake pressure (up to 50 bar/5 MPa) to simulate heavy
braking or overloaded conditions
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ISO/PAS 22596:2022(E)
3.12
low load and pressure section
section (3.6) of test procedure with a series of brake snubs (3.8) to generate a significant amount of wear
debris at low load and brake pressure
4 Symbols and abbreviated terms
4.1 Symbols
Symbol Definition Unit
2
A Total piston area mm
p
2
I Test inertia reflected at the brake kg·m
M Measured torque N·m
d,brake
P Applied pressure kPa
p Threshold pressure or minimum pressure required to develop braking torque kPa
threshold
R Brake effective radius mm
eff
R Dynamic tyre effective rolling radius m
V Prescribed or braking speed for the brake application km/h
p
2
Z Deceleration m/s
μ Average by time friction value for disc brakes —
μ* Instantaneous friction value for disc brakes —
η Brake efficiency %
4.2 Abbreviated terms
DTV Disc Thickness Variation
IBT Initial Brake Temperature (disc)
GVM Gross Vehicle Mass
LRO Lateral Run-Out
MPU Metal Pick-Up
NAO Non-Asbestos Organic
NVH Noise, Vibration and Harshness
5 Test conditions and test preparation
5.1 Inertia for the brake testing
Use inertia calculated based on the real brake force distribution for a deceleration level of 0,3 g (2,94 m/
s²) and GVM vehicle mass conditions.
Option: if the nominal brake force distribution is not known, use the following approach:
— front inertia: calculate the inertia for the front axle using 75 % of half the gross vehicle mass, and
the tyre rolling radius;
— rear inertia: calculate the inertia for the rear axle using 25 % of half the gross vehicle mass and the
tyre rolling radius.
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ISO/PAS 22596:2022(E)
5.2 Pressure ramp rate
The pressure ramp rate shall be 3 MPa/s for all brake applications.
5.3 Maximum pressure
The maximum pressure applied to the brake can be lower than that specified in this document to
accommodate specific brake configurations or brake system design parameters.
5.4 Sampling rate
The sampling rate shall be at least 100 Hz for pressure and torque.
5.5 Initial brake temperature
The initial brake temperature shall be the real-time temperature on the disc at the start of the brake
application.
5.6 Brake temperature measurement
One thermocouple shall be 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 thermocouple.
Additional thermocouple(s) can be in the centre of the outer pad recessed 1 mm into the friction
material. If a slot through the centre is present, the thermocouple shall be at least 5 mm left or right
from the slot (on the radial centre line). Change the thermocouple location towards the trailing (check if
trailing or leading edge) edge of the lining if slots, calliper fingers or other brake features interfere with
placing the thermocouple in the exact centre of the pad.
5.7 Cooling air conditioning
For specific cooling air definition (speed, temperature, humidity) for every test type (wet, heat and
pressure, low temperature and low pressure) refer to the Tables 1 to 4.
Tolerances for cooling air parameters:
— temperature: value ±2 °C (mandatory);
— humidity: ±5 % (optional);
— air speed: ±3 km/h or equivalent air volume (mandatory).
5.8 Cooling air velocity or volume
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The cooling air velocity or volume shall be specified in km/h or m /h, as measured in the duct. The
duct outlet shall be nominally (300 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 B.
5.9 Exhaust conditions
Use exhaust power shall be higher than cooling air power to keep a light under pressure in the test
cabin.
5.10 Conditioning settings for temperature and absolute humidity (humidity ratio)
The cooling air conditioning for temperature (mandatory) and absolute humidity (optional) shall be
reported as the average of all brake events taken at the start of the brake application. The nominal
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ISO/PAS 22596:2022(E)
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cooling air temperature is (20 ± 2) °C and the absolute humidity is 7,29 g/kg (8,68 g/m ) measured at
sea level. Use the appropriate psychometric 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 ± 2) °C and (50 ± 5) % relative humidity (RH).
5.11 Dynamometer rotational speed between brake applications
For specific dynamometer cooling speed for every test type (wet, hot with pressure, low temperature
and low pressure) refer to the Tables 1 to 4.
5.12 Orientation of brake set-up
Use a knuckle fixture style as default. A universal fixture (plate) is an acceptable option; see Figures 1
and 2.
NOTE Reference SAE J3152 for further details on the fixture styles.
Figure 1 — Example of a knuckle fixture
Figure 2 — Example of a universal fixture
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ISO/PAS 22596:2022(E)
The position of the brake on fixture is as on the vehicle as defined by knuckle; in case of universal
fixture the vehicle position is preferable. Keep the orientation during the project duration.
5.13 Direction of air relative to the brake set-up
The test report shall document the airflow inlet regarding direction (vertical or horizontal) and
orientation relative to the vehicle side under test (from forward, rear, top or bottom). Keep the same
orientation during the project duration.
5.14 Wear measurement
Wear measurement is optional. If measured, initial and final disc and lining thickness and mass shall be
measured and recorded. Measurements shall be made with following accuracy:
— lining: 0,01 mm (with ball head) and 0,1 g;
— disc 0,001 mm and 0,1 g.
5.15 Disc lateral run-out
Initial lateral run-out (LRO) shall be set to 50 µm or less when measured 10 mm from the outer diameter
on the outboard friction surface of the brake disc.
5.16 Caliper, disc or drum and pads condition
The brake disc used for the test shall be new and original equipment (OE) level. Generally, use new
calipers. Used calipers are acceptable if agreed for a specific project.
5.17 Hot brake applications
Control the hot brake applications by pressure and initial brake temperature.
5.18 Water specification
Use city water/tap water, preferably with a water container for water temperature conditioning to (15
to 25) °C. The temperature shall be at the same level for the entire duration of the project, per 5.7.
Lower temperatures are acceptable (down to 7 °C).
5.19 Specification of nozzles for water spraying
The nozzles shall have a flow rate of (0,55 ± 0,1) l/min. The spray angle and spray width of the nozzle is:
90°. Other angles and width are possible if required by dyno design or available space.
The water spray pattern shall impact the disc surface equally over its full width. The spray nozzle shall
produce a flat, bar-shaped spray pattern on the target surface.
See Clause 6 for the description of the nozzle setup.
5.20 Saltwater specification
5.20.1 Recommended solution
Use a 5 % solution of sodium chloride (NaCl) per Annex D. See 5.18 for the water specification.
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ISO/PAS 22596:2022(E)
5.20.2 Alternative solutions
The test may use (but it is not recommended) a solution with commercial-grade salt with the following
composition:
— at least 96 % of NaCl;
— less than 0,5 % of each of the following components: calcium chloride, calcium sulphate, calcium
carbonate, magnesium chloride, magnesium sulphate, and potassium chloride;
— a 5 % solution, see 5.18 for the water specification.
5.20.3 Other solutions
The test can use other salt compositions.
EXAMPLE De-icing salt used in Germany: NaCl 92,1 % -MgCl 7,9 %: solution 5 % in water.
2
5.21 Noise and vibration (NVH) measurements
Noise and vibration recording is optional. Simultaneous measurement should help to identify noise
events caused by MPU.
Setup for NVH measurement:
— sampling frequency: at least 44 kHz;
— position of the microphone: 0,5 m above and 0,1 m outboard of the hub;
— position of the accelerometer: leading side of the anchor bracket;
— use Hanning windows with 50 % overlap, for noises up to 20 kHz with 800 spectral lines of resolution.
Brake event is noisy when the frequency difference measured by the microphone and accelerometer is
not greater than 25 Hz.
5.22 Data collection
It is necessary to configure the data collection system of the inertia dynamometer to collect
automatically and in real-time the following values:
a) time,
b) shaft rotational speed (vehicle equivalent speed),
c) hydraulic pressure,
d) brake torque,
e) brake disc temperature,
f) brake fluid displacement,
g) cooling air
...