ISO 14792:2011

Road vehicles — Heavy commercial vehicles and buses — Steady-state circular tests

ISO 14792:2011 specifies tests for determining the steady-state directional control response of heavy vehicles, one of the factors composing vehicle dynamics and road-holding properties. ISO 14792:2011 is applicable to heavy vehicles, i.e. commercial vehicles, combinations, buses and articulated buses as defined in ISO 3833, covered by Categories M3, N2, N3, O3, and O4 of UNECE (United Nations Economic Commission for Europe) and EC vehicle regulations. These categories pertain to trucks and trailers with a maximum mass above 3,5 t and to buses and articulated buses with a maximum mass above 5 t.

Véhicules routiers — Véhicules utilitaires lourds et autobus — Essais sur trajectoire circulaire en régime permanent

General Information

• Status: Published
• Publication Date: 10-Mar-2011
• ICS: 43.080.01 - Commercial vehicles in general
• Technical Committee: ISO/TC 22/SC 33 - Vehicle dynamics and chassis components
• Drafting Committee: ISO/TC 22/SC 33/WG 6 - Vehicle dynamics of heavy commercial vehicles and buses
• Current Stage: 9093 - International Standard confirmed
• Completion Date: 19-Jul-2019

Relations

• Revises: ISO 14792:2003 - Road vehicles — Heavy commercial vehicles and buses — Steady-state circular tests
• Effective Date: 21-Aug-2010

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 14792
Second edition
2011-03-15
Road vehicles — Heavy commercial
vehicles and buses — Steady-state
circular tests
Véhicules routiers — Véhicules utilitaires lourds et autobus — Essais
sur trajectoire circulaire en régime permanent
Reference number
ISO 14792:2011(E)
ISO 2011
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ISO 14792:2011(E)
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ii © ISO 2011 – All rights reserved
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ISO 14792:2011(E)
Contents Page

Foreword ............................................................................................................................................................iv

Introduction.........................................................................................................................................................v

1 Scope......................................................................................................................................................1

2 Normative references............................................................................................................................1

3 Test objectives.......................................................................................................................................1

4 Variables and reference system ..........................................................................................................2

5 Measuring equipment ...........................................................................................................................2

6 Test conditions ......................................................................................................................................2

7 Test procedures.....................................................................................................................................3

7.1 General ...................................................................................................................................................3

7.2 Constant radius test..............................................................................................................................3

7.3 Constant speed, variable-steer angle test ..........................................................................................3

7.4 Common test conditions ......................................................................................................................3

8 Data analysis..........................................................................................................................................4

8.1 General ...................................................................................................................................................4

8.2 Steering-wheel angle.............................................................................................................................4

8.3 Centripetal acceleration........................................................................................................................4

8.4 Curvature of trajectory..........................................................................................................................4

9 Data evaluation and presentation of results ......................................................................................4

9.1 General ...................................................................................................................................................4

9.2 Other evaluations and presentation of results...................................................................................5

Annex A (normative) Test report — Presentation of results..........................................................................8

Bibliography......................................................................................................................................................13

© ISO 2011 – All rights reserved iii
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ISO 14792:2011(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.

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 14792 was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 9, Vehicles

dynamics and road-holding ability.

This second edition cancels and replaces the first edition (ISO 14792:2003), of which it constitutes a minor

revision.
iv © ISO 2011 – All rights reserved
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ISO 14792:2011(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 must necessarily involve 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.
© ISO 2011 – All rights reserved v
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INTERNATIONAL STANDARD ISO 14792:2011(E)
Road vehicles — Heavy commercial vehicles and buses —
Steady-state circular tests
1 Scope

This International Standard specifies tests for determining the steady-state directional control response

of heavy vehicles, one of the factors composing vehicle dynamics and road-holding properties. It is applicable

to heavy vehicles, i.e. commercial vehicles, combinations, buses and articulated buses as defined in ISO 3833,

covered by Categories M3, N2, N3, O3, and O4 of UNECE (United Nations Economic Commission for

Europe) and EC vehicle regulations. These categories pertain to trucks and trailers with a maximum mass

above 3,5 t and to buses and articulated buses with a maximum mass above 5 t.
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 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
3 Test objectives
The general conditions for
⎯ variables,
⎯ measuring equipment and data processing,
⎯ environment (test track and wind velocity),
⎯ test vehicle preparation (tuning and loading),
⎯ initial driving, and
⎯ the reporting of general data and test conditions

of general significance, independent of the specific vehicle dynamics test procedure, shall be as specified in

ISO 15037-2. They shall apply when vehicle dynamics properties are determined unless other conditions are

required in the standard for the test procedure actually used.
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ISO 14792:2011(E)

Although this International Standard is intended for combination vehicles as well as for single-unit vehicles,

Clauses 8 and 9, regarding data analysis, evaluation and presentation, deal only with the motion variables of

the single-unit vehicle or of the first unit of combinations. Thus, in order to comply with this International

Standard, the user shall meet the requirements for variables, measuring equipment and data handling only in

as far as they apply to the single-unit vehicle or to the first unit of combinations. Nevertheless, users are

encouraged to measure and analyse the motions of trailing units as appropriate to their particular purposes.

The primary objective of this test procedure is to determine the steady-state turning characteristics of heavy

vehicles for both left- and right-hand turns.

The steady-state turning behaviour of unit vehicles which have more than two axles and/or dual or wide-base

tyres, as is the case with most heavy vehicles, is known to be a strong function of both centripetal acceleration

[3][4]

and path curvature . To characterize the steady-state behaviour of these vehicles, it is therefore necessary

to conduct turning tests on different radii turns as well as at varying levels of centripetal acceleration. Such a

test program may be accomplished through a series of constant radius tests conducted at various radii, or

through a series of constant speed, variable-steer angle tests conducted at different speeds. Indeed, it is

desirable that both types of tests be conducted for a full characterization of the steady-state turning of these

vehicles.

The constant radius test requires the test vehicle to be driven at a constant speed on a path of known,

constant radius. The directional control response characteristics are determined from data obtained by

repeating the procedure at successively higher speeds. To fully characterize the steady-turning of the vehicle,

this procedure shall then be repeated for various radii. The procedure may be tailored to existing test track

facilities by selecting circles or paths of appropriate radii.

The constant speed, variable-steer angle test requires the test vehicle to be driven at a constant speed and

constant steer angle. The directional control response characteristics are determined from data obtained by

repeating the procedure at successively greater steer angles. To fully characterize the steady-turning of the

vehicle, this procedure shall then be repeated at various speeds.
4 Variables and reference system

The variables to be determined may be selected for test purposes from those given in ISO 15037-2 and shall

be monitored using appropriate transducers. The variables relate to the intermediate axis system (X, Y, Z)

(see ISO 8855).

For the purposes of this International Standard, the reference point shall be the centre of gravity of the vehicle

unit.
This provision overrides the similar provision of ISO 15037-2.

Strictly speaking, the steady-state turning performance ought to be evaluated based on centripetal

acceleration, a , rather than on lateral acceleration, a , (see ISO 8855). In most practical situations, however,

c Y

the difference between these two quantities is small and can be ignored. Nevertheless, in a few cases

(e.g. long-wheelbase vehicles operating on small turning radii or any vehicle operating at large body sideslip

angles), the difference could be appreciable. In these cases, measured lateral acceleration needs to be

corrected for sideslip angle to determine centripetal acceleration. In any case, this document refers to

centripetal acceleration throughout rather than to lateral acceleration.
5 Measuring equipment
The measuring and recording equipment shall be in accordance with ISO 15037-2.
6 Test conditions

The limits and specifications for ambient and vehicle test conditions shall be in accordance with ISO 15037-2.

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ISO 14792:2011(E)
7 Test procedures
7.1 General
The general test specifications shall be in accordance with ISO 15037-2.
7.2 Constant radius test

During this test procedure, the vehicle shall be steered such that it moves on a circular path at a constant

speed. Repeat the procedure at successively faster speeds. The entire procedure should be repeated on

paths of at least three different radii.

A standard radius of 100 m should be used for one of the paths. The radii of the other paths should span the

largest range practicable. The significance of the results improves with increases in the range and number of

radii. Whichever the radii chosen, the vehicle shall be steered such that the reference point of the first unit

remains within 0,5 m of the intended circular path.

For each radius chosen, conduct the test at several speeds. The first speed shall be the slowest practical

speed. Choose successive speeds such that the increments of centripetal acceleration are not more than

0,5 m/s . Where the data vary rapidly with centripetal acceleration, it could be useful to make smaller

incremental changes.
7.3 Constant speed, variable-steer angle test

During this test procedure, the vehicle shall be driven at a constant speed and constant steer angle. Repeat

the procedure at successively larger steer angles. The entire procedure should be repeated applying at least

three different speeds.

The standard speed should be 50 km/h and additional speeds covering the broadest range practicable are

also recommended. A test at a very slow speed is desirable. The significance of the results improves with

increases in the range and number of speeds.

For each test run, maintain the average speed within a tolerance of ± 2 km/h of the selected speed.

A deviation of the vehicle speed of ± 3 km/h from the selected speed is permissible.

For each test speed, conduct tests at several levels of constant steer angle. The first steer angle shall be the

smallest practical deflection from the straight-ahead position. Choose successive steer angles such that the

increments of centripetal acceleration are no more than 0,5 m/s . At slower speeds, where large changes of

steer angle produce little change in centripetal acceleration, it could be useful to make smaller incremental

changes.
7.4 Common test conditions

For each test, maintain the steering-wheel position and the vehicle speed as constant as possible during the

acquisition of the data. Take data for at least 3 s at each steady-state centripetal acceleration. During this time

period, the standard deviation of centripetal acceleration shall not exceed 0,25 m/s .

Take data for both left and right turns. All the data may be taken in one direction followed by all the data in the

other direction. Alternatively, data may be taken successively in one direction and in the other for each

acceleration level, going from the lowest to the highest. Note the method in accordance with Annex A.

The range of centripetal accelerations covered should be as large as is practicable. However, a careful

estimation of the rollover limit of the test vehicle should be made prior to testing. Special care should be taken

whenever centripetal acceleration of a test might exceed 75 % of this estimate. The use of anti-rollover

outriggers should be considered for any
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