ISO 21233:2021

INTERNATIONAL ISO
STANDARD 21233
First edition
Heavy commercial vehicles and
buses — Vehicle dynamics simulation
and validation — Closing-curve test
Véhicule utilitaires lourds et autobus — Simulation et validation
dynamique des véhicules — Essai en courbe fermée
PROOF/ÉPREUVE
Reference number
ISO 21233:2021(E)
©
ISO 2021

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ISO 21233:2021(E)

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© ISO 2021
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Published in Switzerland
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ISO 21233:2021(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Variables . 2
6 Simulation model parameters and requirements . 3
6.1 General . 3
6.2 Basic vehicle parameters. 3
6.3 Estimated vehicle parameters . 3
6.3.1 Principal moments of inertia. 3
6.3.2 Tyre force characteristics . 4
6.3.3 Damper characteristics . 4
6.4 Electronic stability control . 4
6.5 Braking system . 5
6.6 Additional model requirements . 5
7 Physical testing. 5
7.1 General . 5
7.2 Test method . 5
7.3 Evaluation of test results . 6
8 Simulation . 6
8.1 General . 6
8.2 Data recording . 6
8.3 Documentation . 6
9 Comparison of simulation and physical tests . 7
9.1 General . 7
9.2 Dynamic vehicle behaviour without ESC. 7
9.2.1 Wheel lift-off . 7
9.2.2 Comparison of yaw velocity and lateral acceleration . 7
9.3 Dynamic vehicle behaviour with ESC .10
9.3.1 ESC intervention.10
9.3.2 Vehicle behaviour after ESC intervention.11
9.4 ESC safety margin gained from the measurements with and without ESC .12
Annex A (informative) Validation report .13
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ISO 21233:2021(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).
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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 21233:2021(E)

Introduction
The main purpose of this document is to provide a repeatable and discriminatory method for comparing
simulation results to measured test data from a physical vehicle for a specific type of test.
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
interactions of these driver–vehicle–environment elements are each complex in themselves. A complete
and accurate description of the behaviour of the road vehicle involves information obtained from a
number of different tests.
Since this test method quantifies only one small part of the complete vehicle handling characteristics,
the validation method associated with this test can only be considered significant for a correspondingly
small part of the overall dynamic behaviour.
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INTERNATIONAL STANDARD ISO 21233:2021(E)
Heavy commercial vehicles and buses — Vehicle dynamics
simulation and validation — Closing-curve test
1 Scope
This document specifies a method for comparing simulation results from a vehicle model to measured
test data for an existing vehicle according to closing-curve tests as specified in ISO 11026. The purpose
of the validation is to demonstrate that the vehicle dynamics simulation, combined with an integrated
electronic stability control (ESC) system, can predict the roll and yaw stability behaviour of a physical
vehicle, including the ESC system interventions, during a closing-curve test. The simulation method can
be either hardware-in-the-loop [with the original electronic control unit (ECU) on a HiL test stand]
or software-in-the-loop, based on a software code generated from the same source as for the ECU in
the real vehicle. This document applies to heavy vehicles, including commercial vehicles, commercial
vehicle combinations, buses and articulated buses as defined in ISO 3833 (trucks and trailers with a
maximum weight above 3,5 tonnes and buses and articulated buses with a maximum weight above
5 tonnes, according to ECE and EC vehicle classification, categories M3, N2, N3, O3 and O4).
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 3833, Road vehicles — Types — Terms and definitions
ISO 8855, Road vehicles — Vehicle dynamics and road-holding ability — Vocabulary
ISO 15037-2:2002, Road vehicles — Vehicle dynamics test methods — Part 2: General conditions for heavy
vehicles and buses
ISO 11026, Heavy commercial vehicles and buses — Test method for roll stability — Closing-curve test
ISO 19585:2019, Heavy commercial vehicles and buses — Vehicle dynamics simulation and validation —
Steady-state circular driving behavior
3 Terms and definitions
For the purpose of this standard, the terms and definitions given in ISO 3833, ISO 8855, ISO 15037-2,
ISO 11026, ISO 19585 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
software-in-the-loop
SiL
method of integrating the ESC system into the simulation using a software code generated from the
same source as for the vehicle ECU
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ISO 21233:2021(E)

3.2
hardware-in-the-loop
HiL
method of integrating the ESC system into the simulation by incorporating both the vehicle model and
the ECU hardware into a HiL test stand
3.3
ESC intervention time
point in time during a single test where the first ESC (drivetrain or brake) intervention occurs
3.4
intervention steering wheel angle
steering wheel angle at the ESC intervention time (3.3)
3.5
intervention yaw velocity
yaw velocity at the ESC intervention time (3.3)
3.6
intervention lateral acceleration
lateral acceleration at the ESC intervention time (3.3)
3.7
maximum initial velocity
maximum initial driving condition velocity for the test path at which no subsequent wheel lift-off occurs
during the test and at which the vehicle maintains the intended trajectory
4 Principle
The test method defined in ISO 11026 serves to determine the rollover stability of heavy commercial
vehicles and buses as defined in ISO 3833. The test method is designed for vehicles equipped with an
electronic stability system (ESC).
Within this document, the purpose of the closing-curve test validation is to demonstrate that a vehicle
model can predict the vehicle stability behaviour within specified tolerances. The vehicle model is used
to simulate a specific existing vehicle, which is also tested physically, using the test method specified
in ISO 11026. Measurement results are used to define reference curves and characteristic values, and
the respective simulation results are compared to analyse the deviation between physical test and
simulation.
Prior to the validation of the vehicle model for the closing-curve test, a validation for steady-state
cornering according to ISO 19585 shall be conducted. In addition to this basic validation, the validation
done according to this document serves to demonstrate that the vehicle model correctly predicts
wheel lift-off during the closing curve test and that ESC interventions are represented correctly by the
simulation.
5 Variables
The variables of motion used to describe the behaviour of the vehicle shall be related to the reference
axis system (X, Y, Z) of the first vehicle unit (see ISO 8855). For the purpose of this document, the
reference point shall be the centre of gravity (or alternatively the ESC sensor position) of the first
vehicle unit. This provision overrides the similar provision of ISO 15037-2. Measurement requirements
shall be taken from ISO 11026 and ISO 15037-2. The variables that shall be determined for compliance
with this document are:
— longitudinal velocity, v ;
x
— steering-wheel angle, δ ;
H
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ISO 21233:2021(E)

— lateral acceleration, a ;
y

— yaw velocity, ψ ;
— intervention flags (ESC output values) for both drivetrain and brake control;
— desired engine torque limit (ESC output values);
— desired brake torques or desired brake pressures (ESC output values);
— wheel speed sensor signals (as an indication for lift-off of the inner wheels).
It is recommended that the following variables are also determined:
— side slip angle of first vehicle unit;
— roll angle of first vehicle unit;
— steering wheel angle velocity;
— roll angle(s) of the towed vehicle unit(s) at relevant points;
— articulation angle(s) between the vehicle units;
— type of ESC intervention (yaw control or roll stability control);
— vehicle path of the reference point of the first vehicle unit.
For measuring lateral acceleration, yaw velocity and steering wheel angle, it is sufficient to use the ESC
sensor data from the vehicle bus system.
For vehicles with an electrical actuation of the brakes, the desired brake torques shall be determined
instead of the desired brake pressures.
6 Simulation model parameters and requirements
6.1 General
The vehicle model used to predict the behaviour of a vehicle of interest shall include a vehicle model
capable of calculating variables of interest for the test procedures being simulated. In this document,
the vehicle model is used to simulate the closing-curve test method described in 7.2 and to provide
calculated values of the variables of interest from Clause 5.
Prior to the validation of the vehicle model for the closing-curve test, a validation for steady-state
cornering according to ISO 19585 shall be conducted. Correspondingly, all definitions of the simulation
model parameters and requirements included in ISO 19585:2019, Clause 6, shall apply, together with the
following additional specifications for the closing-curve test and the interventions of the ESC system.
6.2 Basic vehicle parameters
The basic vehicle parameters of ISO 19585:2019, 6.2, shall apply.
6.3 Estimated vehicle parameters
The estimated vehicle parameters of ISO 19585:2019, 6.2, shall apply, together with the following
additions.
6.3.1 Principal moments of inertia
The initial values of the principal moments of inertia shall be derived from measurements or design
data and should not be altered more than ±20 % during the validation process.
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6.3.2 Tyre force characteristics
In addition to the definitions specified for the tyre lateral force characteristics in ISO 19585:2019, 6.2,
the tyre model shall be capable of representing the tyre transient force behaviour.
The tyre model of the vehicle model shall include the tyre longitudinal force characteristics and a
representation of the combined lateral and longitudinal slip behaviour in order that the ESC system
brake intervention effects can be simulated. It is recommended that (on a dry and even road surface)
the deviation of the gradient around zero of the tyre longitudinal force versus longitudinal slip used
in the tyre model and the curves of the tyre measurement should not exceed ±20 %. The maximum
value of the longitudinal force of the tyre model should be within ±10 % of the measured value. For this
comparison of characteristic c
...