Heavy commercial vehicles and buses -- Vehicle dynamics simulation and validation -- Closing-curve test

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 ISOÂ 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 ISOÂ 3833 (trucks and trailers with a maximum weight above 3,5Â tonnes and buses and articulated buses with a maximum weight above 5Â tonnes, according to ECE and EC vehicle classification, categories M3, N2, N3, O3 and O4).

Véhicule utilitaires lourds et autobus -- Simulation et validation dynamique des véhicules -- Essai en courbe fermée

General Information

Status
Published
Publication Date
03-May-2021
Current Stage
5060 - Close of voting Proof returned by Secretariat
Start Date
30-Mar-2021
Completion Date
30-Mar-2021
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INTERNATIONAL ISO
STANDARD 21233
First edition
2021-05
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
Reference number
ISO 21233:2021(E)
ISO 2021
---------------------- Page: 1 ----------------------
ISO 21233:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved
---------------------- Page: 2 ----------------------
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

© ISO 2021 – All rights reserved iii
---------------------- Page: 3 ----------------------
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).

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.
iv © ISO 2021 – All rights reserved
---------------------- Page: 4 ----------------------
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.
© ISO 2021 – All rights reserved v
---------------------- Page: 5 ----------------------
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
© ISO 2021 – All rights reserved 1
---------------------- Page: 6 ----------------------
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 ;
— steering-wheel angle, δ ;
2 © ISO 2021 – All rights reserved
---------------------- Page: 7 ----------------------
ISO 21233:2021(E)
— lateral acceleration, a ;
— 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.
© ISO 2021 – All rights reserved 3
---------------------- Page: 8 ----------------------
ISO 21233:2021(E)
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

compar
...

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
---------------------- Page: 1 ----------------------
ISO 21233:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii PROOF/ÉPREUVE © ISO 2021 – All rights reserved
---------------------- Page: 2 ----------------------
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

© ISO 2021 – All rights reserved PROOF/ÉPREUVE iii
---------------------- Page: 3 ----------------------
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).

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.
iv PROOF/ÉPREUVE © ISO 2021 – All rights reserved
---------------------- Page: 4 ----------------------
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.
© ISO 2021 – All rights reserved PROOF/ÉPREUVE v
---------------------- Page: 5 ----------------------
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
© ISO 2021 – All rights reserved PROOF/ÉPREUVE 1
---------------------- Page: 6 ----------------------
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 ;
— steering-wheel angle, δ ;
2 PROOF/ÉPREUVE © ISO 2021 – All rights reserved
---------------------- Page: 7 ----------------------
ISO 21233:2021(E)
— lateral acceleration, a ;
— 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.
© ISO 2021 – All rights reserved PROOF/ÉPREUVE 3
---------------------- Page: 8 ----------------------
ISO 21233:2021(E)
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
...

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