ISO 18375:2016

INTERNATIONAL ISO
STANDARD 18375
First edition
2016-11-15
Heavy commercial vehicles and
buses — Test method for yaw stability
— Sine with dwell test
Véhicules utilitaires lourds et autobus — Méthodes d’essai pour la
stabilité en lacet — Essai de sinus modifié avec pause
Reference number
ISO 18375:2016(E)
©
ISO 2016

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ISO 18375:2016(E)

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ISO 18375:2016(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Measuring equipment . 2
6 Variables . 3
7 Test conditions . 4
7.1 General . 4
7.2 Test track . 4
7.3 Test vehicle . 4
7.3.1 Safety equipment . 4
7.3.2 Loading conditions . . 4
7.3.3 Test equipment . 4
8 Test method . 5
8.1 Initial driving condition . 5
8.2 Determination of the initial steering-wheel angle amplitude . 5
8.3 Performance of the steering procedure. 5
9 Data evaluation . 5
9.1 General . 5
9.2 Characteristic values . 5
Annex A (normative) Test report — General data and test conditions. 9
Annex B (informative) Example of reporting of sine with dwell tests .10
Bibliography .13
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ISO 18375:2016(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
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electrotechnical standardization.
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described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
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The committee responsible for this document is ISO/TC 22, Road vehicles, Subcommittee SC 33, Vehicle
dynamics and chassis components.
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ISO 18375:2016(E)

Introduction
The main purpose of this International Standard is to provide repeatable and discriminatory test
results.
The dynamic behaviour of a road vehicle is a very important aspect of active vehicle safety. Any given
vehicle, together with its driver and the prevailing environment, constitutes a closed-loop system that
is unique. The task of evaluating the dynamic behaviour is, therefore, very difficult since the significant
interaction of these driver vehicle-environment elements are each complex in themselves. A complete
and accurate description of the behaviour of the road vehicle requires information obtained from a
number of different tests.
Since this test method quantifies only one small part of the complete vehicle handling characteristics,
the results of these tests can only be considered significant for a correspondingly small part of the
overall dynamic behaviour.
Moreover, insufficient knowledge is available concerning the relationship between overall vehicle
dynamic properties and accident avoidance. A substantial amount of work is necessary to acquire
sufficient and reliable data on the correlation between accident avoidance and vehicle dynamic
properties in general and the results of these tests in particular. Consequently, any application of this
test method for regulation purposes will require proven correlation between test results and accident
statistics.
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INTERNATIONAL STANDARD ISO 18375:2016(E)
Heavy commercial vehicles and buses — Test method for
yaw stability — Sine with dwell test
1 Scope
This International Standard describes an open-loop test method for determining the yaw stability
of a vehicle on a low friction road surface. It applies to heavy vehicles, that is commercial vehicles,
commercial vehicle combinations, buses and articulated buses as defined in ISO 3833 (trucks and
trailers with maximum weight above 3,5 tonnes and buses and articulated buses with maximum weight
above 5 tonnes, according to ECE and EC vehicle classification, categories M3, N2, N3, O3 and O4).
The method is intended for vehicles equipped with electronic yaw-stability control systems.
As the results of this test depend largely on local and temporary changes in road surface friction, this
International Standard gives recommendations about keeping the friction level as uniform as possible
for good reproducibility of the test results.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 15037-2:2002, Road vehicles — Vehicle dynamics test methods — Part 2: General conditions for heavy
vehicles and buses
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 8855, ISO 15037-2 and the
following apply.
3.1
beginning of steer input
T
0
time when the steering-wheel angle input is started
3.2
end of steer input
T
1
time when the steering-wheel angle returns to zero at the completion of the sine with dwell steer input
3.3
dwell time
T
d
time interval when the steer input remains constant at absolute maximum amplitude
3.4
steer frequency
f
1
f =
TT−−T
10 d
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ISO 18375:2016(E)

3.5
maximum steady-state lateral acceleration
maximum lateral acceleration that the vehicle can sustain for the selected test surface during steady-
state cornering at the selected constant longitudinal velocity without yaw or roll instability when the
electronic stability control system is disabled.
3.6
steady-state steering-wheel angle amplitude
δ
Hss
smallest steering-wheel angle amplitude at maximum steady-state lateral acceleration (3.5)
3.7
time delay
DT
i
time difference between the yaw velocity of the i:th unit and the yaw velocity of the first unit at their
first zero crossing when performing the sine with dwell with steady-state steering-wheel angle
amplitude, δ , when 05, / fT+< tT<
Hss
01
4 Principle
The objective of this test method is to study the yaw-stability control of a vehicle on a low friction
surface with a selected initial longitudinal velocity, v , which is subjected to a steering-wheel input
x0
by a steering machine. The steer input is a sine with dwell of steer frequency, f, and dwell time, T , as
d
shown in Figure 1. The steering-wheel angle amplitude, δ , is increased in steps until yaw instability
Η
occurs. The results are evaluated with respect to responsiveness, yaw stability, and yaw angle after
completion of steer.
Key
X time
Y steering wheel angle
Figure 1 — Steering-wheel angle input
5 Measuring equipment
The measuring equipment, transducer installation, and data processing shall be in accordance with
ISO 15037-2.
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ISO 18375:2016(E)

6 Variables
The variables that shall be determined for compliance with this International Standard are the
following:
— steering-wheel angle, δ ;
H
— longitudinal velocity, v ;
x
— lateral acceleration, a ;
y

— yaw velocity of each unit,ψ ;
i
— yaw angle of the first unit,ψ ;
1
— lateral displacement of the first vehicle unit’s first axle, Y ;
1
— indication of intervention of the electronic stability control system (e.g. roll and yaw);
— articulation angles between vehicle units, Δψ ;
i
— indication of the engagement of the anti-jack-knife device.
It is recommended that the following variables also be determined:
— global position of the first vehicle unit;
— lateral velocity, v , and/or body side slip angle, β, of the first unit;
y
— roll angle and roll rate;
— longitudinal acceleration, a ;
x
— wheel brake pressures, p ;
B
— rotational velocity of wheels, ω ;
i
— re
...