ISO 4138:1996
(Main)Passenger cars — Steady-state circular driving behaviour — Open-loop test procedure
Passenger cars — Steady-state circular driving behaviour — Open-loop test procedure
Describes an open-loop test procedure to determine the steady state directional control response of passenger cars.
Voitures particulières — Tenue de route en régime permanent sur trajectoire circulaire — Méthode d'essai en boucle ouverte
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Standards Content (Sample)
INTERNATIONAL
STANDARD 4138
Second edition
1996-12-15
Passenger cars - Steady-state circular
driving behaviour - Open-loop test
procedure
Voitures particulikes - Tenue de route en Ggime permanent sur
trajectoire circulaire - M&hode d’essai en boucle ouverte
Reference number
IS0 4138:1996(E)
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IS0 4138:1996(E)
Foreword
IS0 (the International Organization for Standardization) is a worldwide
federation of national standards bodies (IS0 member bodies). The work of
preparing International Standards is normally carried out through IS0
technical committees. Each member body interested in a subject for which
a technical committee has been established has the right to be rep-
resented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. IS0
collaborates closely with the International Electrotechnical Commission
(IEC) on all matters of electrotechnical standardization.
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.
International Standard IS0 4138 was prepared by Technical Committee
ISODC 22, Road vehicles, Subcommittee SC 9, Vehicle dynamics and
road-holding ability.
This second edition cancels and replaces the first edition (IS0 4138:1982),
which has been technically revised.
Annexes A and B form an integral part of this International Standard.
0 IS0 1996
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced
or utilized in any form or by any means electronrc or mechanical, including photocopying and
microfilm, without permission in writing from the publisher,
International Organization for Standardization
Case postale 56 l CH-1211 Geneve 20 l Switzerland
Printed in Switzerland
ii
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@ IS0 IS0 4138:1996(E)
Introduction
The dynamic behaviour of a road vehicle is a most important part of the
active vehicle safety. Any given vehicle, together with its driver and the
prevailing environment, constitutes a closed-loop system which is unique.
The task of evaluating the dynamic behaviour is therefore very difficult
since the significant interaction of these driver-vehicle-road elements are
each complex in themselves. A description of the behaviour of the road
vehicle must inevitably involve information obtained from a number of
tests of different types.
Since the steady-state circular test procedure quantifies only one small
part of the complete handling characteristics, the results of this test 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
large 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 this test in particular. Therefore, it is not
possible to use this procedure and test results for regulation purposes.
To desc ribe the circula driving behavi our of pass enger cars in steady-state
n there are fou known differe
conditio nt test met hods:
- constant radius test;
- constant steer angle test;
- constant speed, variable steer angle test;
- constant speed, variable radius test.
IS0 4138 defines only the constant radius test method.
. . .
III
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BNTERNATIONAL STANDARD 0 IS0 IS0 4138:1996(E)
Passenger cars - Steady-state circular driving behaviour -
Open-loop test procedure
I Scope
This lnternational Standard defines an open-loop test procedure to determine the steady state directional control
response of passenger cars by measuring the steady-state cornering behaviour which is one of the factors
composing vehicle dynamics and road holding properties.
It applies to passenger cars as defined in IS0 3833.
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of this
International Standard. At the time of publication, the editions indicated were valid. All standards are subject to
revision, and parties to agreements based on this International Standard are encouraged to investigate the
possibility of applying the most recent editions of the standards indicated below. Members of IEC and IS0
maintain registers of currently valid International Standards.
IS0 1176: 1990, Road vehicles - Masses - Vocabulary and codes.
IS0 2416:
1976, Passenger cars - Mass distribution.
IS0 3833: 1977, Road vehicles - Types - Terms and definitions.
IS0 8855:1991, Road vehicles - Vehicle dynamics and road-holding ability - Vocabulary.
3 Principle
The purpose of this test procedure is to measure the steering-wheel angle as a function of lateral acceleration and
to describe vehicle steering (for example, understeer/oversteer) behaviour for left-hand and right-hand turns.
This procedure requires the test vehicle to be driven at several constant (see 7.2) speeds on a path of known
radius. The directional control response characteristics are determined from data obtained while driving the vehicle
at successively higher speeds on the constant radius path (or path of sufficent length to attain steady state). This
procedure can be conducted in a relatively small area. The procedure can be tailored to existing test track facilities
by selecting a circle or path of appropriate radius. Often a constant radius (in plane) road will suffice for a test
facility.
The variables of motion used to describe the steady state directional control response of the vehicle relate to the
intermediate axis system X, Y, 2 (see IS0 8855).
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IS0 4138:1996(E)
The location of the origin of the intermediate axis system, being the reference point, is independent from loading
condition. It is fixed in the longitudinal plane of symmetry at half wheel base and at the same height above the
ground as the centre of gravity of the vehicle at complete vehicle kerb mass (see IS0 1176).
4 Variables
The following variables corresponding to the terms and definitions of IS0 8855 shall be measured:
- steering-wheel angle, (&;
- lateral acceleration, ay.
NOTE 1 Alternatively, lateral acceleration may be determined from other variables.
NOTE 2 Strictly speaking, test results based on lateral acceleration should not be used for comparison of the performance of
different vehicles. This is because lateral acceleration, as precisely defined, is measured at right angles to the intermediate
X-axis and not at right angles to the tangent of the vehicle path. To overcome this difficulty, lateral acceleration may be
corrected for vehicle sideslip angle, which gives the quantity centripetal acceleration (see clause 8.3). However, the extent of
this correction is not likely to exceed a few percent and can generally be neglected.
It is recommended to measure the following variables as well:
- sideslip angle, p;
If the whole procedure described in clause 9 is to be followed, the sideslip angle must be measured directly or
calculatd from other measured variables.
- yaw velocity, !P ;
- longitudinal velocity, vx;
- steering-wheel torque, M,;
- vehicle roll angle, q.
5 Measuring equipment
5.1 Description
The variables selected from those listed in clause 4 shall be measured by means of appropriate transducers and
their time histories recorded by a multi-channel recorder. The typical operating ranges and recommended
maximum errors of the transducer and recording system are shown in table 1. The values in table 1 are tentative
and provisional until more experience and data are available.
Table 1 - Variables, typical operating ranges and recommended maximum errors
Recommended maximum error
Typical operating range
Variable
of the combined transducer and
recorder system
Steering-wheel angle - 360” to + 360” + Z”, for angles c 180”
& 4’, for angles > 180”
Yaw velocity - 5o”/s to + 5O”/s + 0,5”/s
Sideslip angle - 15” to + 15” + 0,5O
0 m/s to 50 m/s + 0,5 m/s
Longidutinal velocity
Lateral acceleration - 15 m/s* to + 15 m/s* + 0,15 m/s*
Steering-wheel torque - 30 N.m to + 30 N-m + 0,3 N-m
- 15O to + 15O &0,15”
Roll angle
NOTE - Transducers for measuring some of the listed variables are not widely available and are not in
general use. Many such instruments are developed by users. If any system error exceeds the recommended
maximum value, this and the actual maximum error shall be stated in the test report (see annex A).
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5.2 Transciucer installation
instructions exist, so
The transducers shall be installed according to the manufacturer’s instructions where such
determined.
that the variables corresponding to the terms and definitions of IS0 8855 can be
If the transducer does not measure the values directly, appropriate transformations into the reference system shall
be carried out.
5.3 Data processing
The frequency range relevant for this test is between 0 Hz and the maximum utilized frequency of f;nax = 5 Hz.
According to the chosen data processing method, analog or digital, the stipulations given in 5.3.1 or 5.32 shall be
observed.
5.3.1 Analog data processing
The bandwidth of the entire combined transducer/recording system shall be no less than 8 Hz.
In order to execute the necessary filtering of signals, low-pass filters with order four or higher shall be empioyed.
The width of the passband frequency fo at -3 dB shall not be less than 8 Hz. Amplitude errors shall be less than
+ 0,5 % in the relevant frequency range of 0 Hz to 5 Hz. All analog signals shall be processed with filters, having
sufficiently similar phase characteristics, in order to ensure that time delay differences due to filtering shall lie
within the required accuracy for time measurement.
NOTE - Phase shifts may occur during analog filtering of signals with different frequency contents. Therefore a data
processing method, as described in 5.32, is preferable.
5.32 Digital data processing
5.3.2.1 Preparation of analog signals
In order to avoid aliasing, the analog signals shall correspondingly be filtered before digitizing. In this case, low-pass
filters with order four or higher shall be employed. The width of the passband (frequencyfo at -3 dB) shall amount
to roughly
The amplitude error of the anti-aliasing filter should not exceed + 0,5 % in the utilized frequency range from zero to
max. All analog signals shall be processed with anti-aliasing filters having sufficiently similar phase characteristics in
f
order to ensure that time delay differences lie within the required accuracy for time measurement.
Additional filters shall be avoided in the data acquisition string.
Amplification of the signals shall be such that, in relation with the digitizing process, the additionai error is less than
0,2 %.
5.3.2.2 Digitizing
The sampling ratef, shall be appropriate to the order of the filters being used and shall under no circumstances be
less than 2f0.
In common practice anti-aliasing filters of Butterworth type are used. For this type of filter the following
NOTE -
specifications are recommended:
four pole filter: $s 2 sfo
eight pole filter: fs 2 3,6fo
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IS0 4138:1996(E)
5.3.2.3 Digital filtering
For filtering of sampled data in data evaluation, phaseless (zero phase shift) digital filters shall be used incorporating
the following characteristics (see figure 1):
- passband range, 2 0 Hz to 2 5 Hz;
- start of stopband, >lOHzand~15Hz;
- filter gain in the passband, 1 k 0,005 (100 % + 0,5 %);
- filter gain in the stopband, s 0,Ol (G 1 %).
Stopband
-
Frequency,Hz
Figure 1 - Required characteristics of phaseless digital filters
6 Test conditions
Limits and specifications for the ambient and vehicle test conditions are established in 6.1 to 6.3, and shall be
maintained during the test. Any deviations shall be shown in the test report (see annex A), including the individual
diagrams of the presentation of results (see annex B).
NOTE - The ambient temperature may influence both the road friction and the tyre characteristics. Therefore the tests
should be carried out without the ambient temperature varying too much.
6.1 Test track
All tests shall be carried out on a level, clean, dry and uniform hard road surface, which must not exceed a gradient
of 2,5 % at any place. For standard test conditions, a smooth dry road surface of asphalt or concrete or a high
friction test surface is recommended.
6.2 Wind velocity
The wind velocity shall not exceed 5 m/s and shall be recorded in the test report (annex A).
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6.3 Test vehicle
6.3.1 Tyres
For standard tyre condition, new tyres shall be fitted on the test vehicle according to the manufacturer’s
specifications. They shall have a tread depth of at least 90 % of the original value and shall be manufactured not
more than one year before the test. The date of manufacture shall be noted in the test report (see annex A).
Tyres shall be inflated to the pressure as specified by the vehicle manufacturer for the test vehicle configuration at
the ambient temperature. The tolerance for setting the cold pressure is t 5 kPal) for pressures up to 250 kPa and
+ - 2 % for pressure above 250 kPa.
They shall be run in for at least 150 km without excessively harsh use, for example braking, acceleration, cornering,
hitting the kerb, etc. After the tyres have been run in, they should remain in the same position on the vehicle for
the test.
The test may also be performed with tyres in any state of wear as long as the end of the test they are in such a
condition that a minimum of I,6 mm of tread depth remains across the whole breadth of the tread (see note) and
around the whole circumference of tyre.
NOTES
1 Tread breadth is the width of that part of the tread which with the tyre correctly inflated contacts the road in normal
straight-line driving.
2 Asin certai n cases the tread depth has a significan t in fluence 0 n test results, it is recommended that it should be taken into
en vehicles or betwee n tyres.
account when making comparisons betwe
6.3.2
Operating components
For the standard test conditions, all operating components likely to influence the results of this test (for example
condition, setting and temperature of shock absorbers, springs and other suspension components and suspension
geometry) shall be as specified by the manufacturer. Any deviations from the manufacturer’s specification shall be
noted in the test report (see annex A).
6.3.3 Drivetrain
For the standard test conditions, the adjustment and condition of the drivetrain (especially the differentials,
clutches, locks, free wheel shifts, etc.) shall correspond to the vehicle manufacturer’s specifications.
6.3.4 Loading conditions of the vehicle
The test mass shall be between complete vehicle kerb mass (code: ISO-M06) plus driver’s mass and maximum
authorized total mass (code: ISO-M08). The instrumentation plus driver should not exceed 150 kg.
The maximum authorized total mass and the maximum design axle loads (code: ISO-M13) shall not be exceeded.
Care shall be taken to generate the minimum deviation in the location of the centre of gravity and in the values of
the moments of inertia as compared to the loading conditions of the vehicle in normal use. The resulting wheel
loads shall be determined and recorded in the test report (annex A).
1) 1kPa = IO-* bar = IO3 N/m*
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IS0 4138:1996(E)
7 Test procedure
7.ll Tyre warm-up
The tyres shall be warmed up in order to achieve a tyre temperature and pressure representative of normal driving
conditions. This should be done by driving at a speed of 100 km/h over a distance of at least 10 km. However, if
this is not practical, this can be done by driving 500 m at a lateral acceleration of 3 m/s* on the radius to be used
for the tests. The tyre pressures after warm-up should be recorded.
7.2 Initial driving condition
During this procedure the vehicle is to be steered in such a manner that the reference point of the vehicle moves
on a circular path. The standard radius of the path shall be 100 m, but larger and smaller radii may be used with
40 m as the recommended lower value and 30 m as the minimum.
The vehicle shall be dr ,iven on the desired circle at the lowest possible speed. Data shall be recorded with the
stee ring-wh eel position and throttle position fixed.
The vehicle shall then be driven at the next speed at which data are to be taken. However, if the instrumentation
requires to be reset between the tests, the vehicle may be stopped for this purpose. Data shall be taken in
increments of the lateral acceleration of not more than 0,5 m/s*. Where the data vary rapidly with lateral
acceleration, it may be useful to take data in smaller increments.
At each lateral acceleration level, the steering-wheel position and throttle position shall be maintained as constant
as possible while data are taken. Whatever radius is chosen, the path shall be followed to within 0,5 m of either
side. Data shall be taken for at least 3 s at each steady-state lateral acceleration level. It is recommended that the
highest gear compatible with the conditions of the test should be used.
NOTE - It may be possible to carry out the test by accelerating very s lowly th rough the speed range and recording the
his can be sp ecif ied as an al ternative procedu re.
variables continuously. Further work is required before t
The value of the lateral acceleration shall be increased and data shall be taken until it is no longer possible to
maintain steady-state conditions.
Data shall be taken for both left and right turns. All the data may be taken in one direction followed by
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