ISO 7401:2011

INTERNATIONAL ISO
STANDARD 7401
Third edition
2011-04-15
Road vehicles — Lateral transient
response test methods — Open-loop test
methods
Véhicules routiers — Méthodes d'essai de réponse transitoire
latérale — Méthodes d'essai en boucle ouverte

Reference number
©
ISO 2011
©  ISO 2011
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ii © ISO 2011 – All rights reserved

Contents Page
Foreword .iv
Introduction.v
1 Scope.1
2 Normative references.1
3 Terms and definitions .1
4 General conditions.1
5 Principle .2
6 Reference system.3
7 Variables.3
8 Measuring equipment .4
9 Test conditions.4
10 Step input .5
11 Sinusoidal input — one period (see ISO/TR 8725) .7
12 Random input (see ISO/TR 8726) .9
13 Pulse input .11
14 Continuous sinusoidal input.12
Annex A (normative) Test report — General data .14
Annex B (normative) Test report — Presentation of results .16
Bibliography.22

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 7401 was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 9, Vehicle
dynamics and road-holding ability.
This third edition cancels and replaces the second edition (ISO 7401:2003), which has been technically
revised.
iv © ISO 2011 – All rights reserved

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 is each complex in itself. 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.
INTERNATIONAL STANDARD ISO 7401:2011(E)

Road vehicles — Lateral transient response test methods —
Open-loop test methods
1 Scope
This International Standard specifies open-loop test methods for determining the transient response behaviour
of road vehicles. It is applicable to passenger cars, as defined in ISO 3833, and to light trucks.
NOTE The open-loop manoeuvres specified in this International Standard are not representative of normal driving
conditions, but are nevertheless useful for obtaining measures of vehicle transient behaviour in response to several specific
types of steering input under closely controlled test conditions. For measurements of steady-state properties, see ISO 4138.
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 1176:1990, Road vehicles — Masses — Vocabulary and codes
ISO 2416:1992, Passenger cars — Mass distribution
ISO/TR 8725:1988, Road vehicles — Transient open-loop response test method with one period of sinusoidal
input
ISO/TR 8726:1988, Road vehicles — Transient open-loop response test method with pseudo-random steering
input
1)
ISO 8855 , Road vehicles — Vehicle dynamics and road-holding ability — Vocabulary
ISO 15037-1:2006, Road vehicles — Vehicle dynamics test methods — Part 1: General conditions for
passenger cars
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 8855 apply.
4 General conditions
The general conditions specified in ISO 15037-1 shall apply.

1) To be published.
5 Principle
5.1 General
IMPORTANT — The method of data analysis in the frequency domain assumes that the vehicle has a
linear response; this is unlikely to be the case over the whole range of lateral accelerations of interest.
The standard method of dealing with such a situation is to restrict the input to a sufficiently small
range such that linear behaviour can be assumed. If necessary, testing can be performed with several
ranges of inputs that, together, cover the entire range of interest.
The primary object of these tests is to determine the transient response behaviour of a vehicle. Characteristic
values and functions in the time and frequency domains are considered necessary for characterizing vehicle
transient response.
Important characteristics in the time domain are:
a) time lags between steering-wheel angle, lateral acceleration and yaw velocity;
b) response times of lateral acceleration and yaw velocity (see 10.2.1 and 10.2.2);
c) lateral acceleration gain (lateral acceleration divided by steering-wheel angle);
d) yaw velocity gain (yaw velocity divided by steering-wheel angle); and
e) overshoot values (see 10.2.3).
These characteristics show correlation with subjective evaluation during road driving.
Important characteristics in the frequency domain are the frequency responses, i.e. amplitudes and phases of:
⎯ lateral acceleration related to steering-wheel angle; and
⎯ yaw velocity related to steering-wheel angle.
5.2 Test methods
There are several test methods for obtaining these characteristics in the domains of time and frequency, the
applicability of which depends in part on the size of the test track available.
a) Time domain:
1) step input; and
2) sinusoidal input (one period).
b) Frequency domain:
1) random input;
2) pulse input; and
3) continuous sinusoidal input.
These test methods are optional, but at least one of each domain type should be performed. The methods
chosen shall be indicated in the general data specified in Annex A and in the presentation of test results
specified in Annex B.
2 © ISO 2011 – All rights reserved

It is possible that the characteristic values of lateral acceleration gain and yaw velocity gain, obtained by the
different test methods, may not be comparable, owing to one or more of the following circumstances:
⎯ linear versus non-linear vehicle behaviour;
⎯ periodic versus non-periodic steady-state condition;
⎯ steady state versus dynamic vehicle behaviour.
6 Reference system
The reference system specified in ISO 15037-1 shall apply.
The location of the origin of the vehicle axis system (X , Y , Z ) is the reference point and therefore should be
V V V
independent of the loading condition. It is fixed in the longitudinal plane of symmetry at half-wheelbase and at
the same height above the ground as the centre of gravity of the vehicle at complete vehicle kerb mass
(see ISO 1176).
7 Variables
The following variables shall be determined:
a) steering-wheel angle, δ ;
H
b) lateral acceleration, a ;
Y

c) yaw velocity, ψ;
d) longitudinal velocity, v .
X
The following variables may be determined:
⎯ roll angle, φ;
⎯ sideslip angle, β;
⎯ lateral velocity, v ;
Y
⎯ steering-wheel torque, M .
H
These variables, defined in ISO 8855, are not intended to comprise a complete list.
8 Measuring equipment
8.1 Description
Subclause 4.1 of ISO 15037-1:2006 shall apply as well as the following additions shown in Table 1.
Table 1 — Variables, typical operating ranges and recommended maximum errors
Recommended maximum error
Variable Range of the combined transducer/
recorder system
a
Steering-wheel angle −180° to +180° ±1°
Yaw velocity −50 °/s to +50 °/s ±0,5 °/s
Lateral velocity −10 m/s to +10 m/s ±0,1 m/s
Sideslip angle −15° to +15° ±0,3°
a
Assuming a conventional steering system.

The use of a programmable steer robot may help to increase the accuracy and repeatability of steer inputs for
the described transient response manoeuvres.
8.2 Transducer installation
Subclause 4.2 of ISO 15037-1:2006 shall apply.
8.3 Data processing
The recording system and data processing requirements contained in 4.3 of ISO 15037-1:2006 shall apply.
9 Test conditions
9.1 General
The test conditions specified in Clause 5 of ISO 15037-1:2006 shall apply.
9.2 Vehicle loading conditions
9.2.1 General
Tests shall be carried out at the minimum loading condition and at the maximum loading condition defined
below, and at other loading conditions of interest.
In accordance with ISO 1176:1990, 4.8 and 4.13, the maximum authorized total mass (Code: ISO-M08) and
the maximum authorized axle load (Code: ISO-M13) shall not be exceeded.
Care shall be taken to minimize the difference of both the location of the centre of gravity and the moments of
inertia as compared to the loading conditions of the vehicle in normal use (see ISO 2416:1992, Clause 4). The
resulting static wheel loads shall be determined and recorded in the test report (see Annex A).
4 © ISO 2011 – All rights reserved

9.2.2 Minimum loading condition
For the minimum loading condition, the total vehicle mass shall consist of the complete vehicle kerb mass
(Code: ISO-M06) in accordance with ISO 1176:1990, 4.6, plus the masses of the driver and the
instrumentation. The mass of the driver and the instrumentation should not exceed 150 kg. The load
distribution shall be equivalent to that of two occupants in the front seats, in accordance with ISO 2416.
9.2.3 Maximum loading condition
For the maximum loading condition, the total mass shall be equal to the max
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