ISO 14793:2011

INTERNATIONAL ISO
STANDARD 14793
Second edition
2011-02-15
Road vehicles — Heavy commercial
vehicles and buses — Lateral transient
response test methods
Véhicules routiers — Véhicules utilitaires lourds et autobus —
Méthodes d'essai de réponse transitoire latérale

Reference number
©
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 Principle .2
5 Reference system.2
6 Variables.3
7 Measuring equipment .3
7.1 Description.3
7.2 Transducer installation.3
7.3 Data processing.3
8 Test conditions .7
8.1 General .7
8.2 Test track.7
8.3 Weather conditions .7
8.4 Test vehicle .8
8.5 Warm-up .9
8.6 Test speed.9
8.7 Lateral acceleration.9
8.8 Average longitudinal acceleration.10
9 Step input .10
9.1 Test procedure.10
9.2 Data analysis.10
9.3 Data presentation .11
10 Sinusoidal input — One period (see ISO/TR 8725) .12
10.1 Test procedure.12
10.2 Data analysis.12
10.3 Data presentation .13
11 Random input (see ISO/TR 8726) .13
11.1 Test procedure.13
11.2 Data analysis.14
11.3 Data presentation .14
12 Pulse input .15
12.1 Test procedure.15
12.2 Data analysis.15
12.3 Data presentation .15
13 Continuous sinusoidal input.16
13.1 Test procedure.16
13.2 Data analysis.16
13.3 Data presentation .17
Annex A (normative) Test report — General data .18
Annex B (normative) Test report — Presentation of results.24
Bibliography.29

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 14793 was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 9, Vehicle
dynamics and road-holding ability.
This second edition cancels and replaces the first edition (ISO 14793:2003), 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 14793:2011(E)

Road vehicles — Heavy commercial vehicles and buses —
Lateral transient response test methods
1 Scope
This International Standard specifies test methods for determining the transient response behaviour of heavy
commercial vehicles, heavy commercial vehicle combinations, buses and articulated buses, as defined in
ISO 3833 for trucks and trailers above 3,5 t and buses above 5 t maximum weight, and in UNECE (United
Nations Economic Commission for Europe) and EC vehicle classification, categories M3, N2, N3, O3 and O4.
NOTE The open-loop manoeuvres specified in this International Standard are not representative of real driving
conditions, but are nevertheless useful for obtaining measures of vehicle transient behaviour — particularly with respect to
that which the driver experiences — in response to several specific types of steering input under closely controlled test
conditions. For combinations where the response of the last vehicle unit is of importance, see ISO 14791.
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 3833:1977, Road vehicles — Types — Terms and definitions
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
ISO 8855:1991, Road vehicles — Vehicle dynamics and road-holding ability — Vocabulary
ECE Regulation No. 30, Uniform provisions concerning the approval of pneumatic tyres for motor vehicles and
their trailers
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 8855 and the following apply.
3.1
vehicle unit
unit of a vehicle combination which is connected with a yaw-articulation joint
EXAMPLE Tractor, semitrailer, dolly.
NOTE The number of vehicle units is one more than the number of articulation joints.
4 Principle
IMPORTANT — The method of data analysis in the frequency domain is based on the assumption that
the vehicle has a linear response. Over the whole range of lateral acceleration this is unlikely to be the
case, the standard method of dealing with such a situation being to restrict the range of the input so
that linear behaviour can be assumed and, if necessary, to perform more than one test at different
ranges of inputs which, together, cover the total range of interest.
The objective of these tests is to determine the transient response of a vehicle. Characteristic values and
functions of both linear and nonlinear behaviour are considered necessary for fully characterizing vehicle
transient response. Linear characteristic values and functions are determined with tests in the frequency
domain and nonlinear characteristic values and functions with tests in the time domain. In the case of vehicle
combinations, it is primarily the response of the first vehicle unit that is evaluated.
Important characteristics in the time domain are
⎯ time lags between steering-wheel angle, lateral acceleration and yaw velocity,
⎯ response times of lateral acceleration and yaw velocity (see 9.2.1),
⎯ lateral acceleration gain (lateral acceleration divided by steering-wheel angle),
⎯ yaw velocity gain (yaw velocity divided by steering-wheel angle), and
⎯ overshoot values (see 9.2.3).
Important characteristics in the frequency domain are the transfer functions of
⎯ lateral acceleration related to steering-wheel angle, and
⎯ yaw velocity related to steering-wheel angle,
expressed as gain and phase functions between input and output variables.
There are several test methods for obtaining these characteristics in the time and frequency domains, as
follows, the applicability of which depends in part on the size of the test track available.
a) time domain:
1) step input;
2) sinusoidal input (one period).
b) frequency domain:
1) random input;
2) pulse input;
3) continuous sinusoidal input.
5 Reference system
The variables of motion used to describe the vehicle behaviour in a test-specific driving situation relate to the
intermediate axis system (X, Y, Z) (see ISO 8855).
The location of the origin of the vehicle axis system (X , Y , Z ) is the reference point and shall be thus
V V V
defined.
2 © ISO 2011 – All rights reserved

6 Variables
The following variables shall be determined:

⎯ yaw velocity, ψ ;
⎯ lateral acceleration, a ;
Y
⎯ steering-wheel angle, δ ;
H
⎯ longitudinal velocity, v .
X
The following variables may be determined:
⎯ lateral deviation, y;
⎯ roll angle at relevant points, ϕ;
⎯ steering-wheel torque, M ;
H
⎯ sideslip angle, β.
These variables, all but lateral deviation defined in ISO 8855, are not intended to comprise a complete list.
7 Measuring equipment
7.1 Description
The variables to be determined in accordance with Clause 6 shall be measured by means of appropriate
transducers. Their time histories shall be recorded on a multi-channel recording system having a time base.
The typical operating ranges and recommended maximum errors of the transducers and the recording system
are given in Table 1.
7.2 Transducer installation
The transducers shall be installed so that the variables corresponding to the terms and definitions of ISO 8855
can be determined.
If the transducer does not measure the variable directly, appropriate transformations into the reference system
shall be carried out.
7.3 Data processing
7.3.1 General
The frequency range relevant for this test is between 0 Hz and the maximum utilized frequency of f = 2 Hz.
max
Depending on the data processing method chosen (analog or digital data processing) the provisions of 7.3.2
or 7.3.3 shall be observed.
For lighter trucks it may be necessary to increase f to 3 Hz. In this case, the following requirements
max
concerning the frequency f may be modified correspondingly.
max
7.3.2 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 of order four or higher shall be employed.
The width of the passband (from 0 Hz to frequency f at −3 dB) shall be not less than 9 Hz. Amplitude errors
shall be less than ± 0,5 % in the relevant frequency range of 0 Hz to 2 Hz. All analog signals shall be
processed with filters having phase characteristics sufficiently similar to ensure that time delay differences due
to filtering lie within the required accuracy for time measurement.
NOTE During analog filtering of signals with different frequency contents, phase shifts can occur. Therefore, a digital
data processing method, as described in 7.3.3, is preferable.
Table 1 — Variables, their typical operating ranges and recommended maximum errors
Variable Range Recommended maximum error of
combined transducer and recorder system
Yaw velocity − 50°/s to + 50°/s ± 0,5°/s
2 2 2
Lateral acceleration − 15 m/s to + 15 m/s ± 0,15 m/s
Steering-wheel angle − 360° to + 360° ± 2° for angles < 180°
± 4° for angles > 180°
Longitudinal velocity 0 m/s to 35 m/s ± 0,35 m/s
Roll angle − 15° to + 15° ± 0,15°
Side slip angle − 10° to + 10° ± 0,3°
Lateral velocity − 10 m/s to + 10 m/s ± 0,1 m/s
Steering-wheel torque
without power steering − 50 N·m to + 50 N⋅m ± 0,5 N⋅m
with power steering − 20 N·m to + 20 N⋅m ± 0,2 N⋅m
Transducers for 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 under general data in the test report (see Annex A).

7.3.3 Digital data processing
7.3.3.1 General considerations
Preparation of analog signals includes consideration of filter amplitude attenuation and sampling rate in order
to avoid aliasing errors, and filter phase lags and time delays. Sampling and digitizing considerations include
presampling amplification of signals so as to minimize digitizing errors, the number of bits per sample, the
number of samples per cycle, sample and hold amplification, and timewise spacing of samples.
Considerations for additional phaseless digital filtering include the selection of passbands and stopbands, and
the attenuation and allowable ripple in each, as well as correction of anti-alias filter phase lags. Each of these
factors shall be considered so that an overall data-acquisition accuracy of ± 0,5 % is achieved.
7.3.3.2 Aliasing errors
In order to avoid uncorrectable aliasing, the analog signals shall be appropriately filtered before sampling and
digitizing. The order of the filters used and their passband shall be chosen according to both the required
flatness in the relevant frequency range and the sampling rate. The minimum filter characteristics and
sampling rate shall be such that
⎯ within the relevant frequency range of 0 Hz to f = 2 Hz the attenuation is less than the resolution of the
max
data acquisition system, and
⎯ at one-half the sampling rate (i.e. the Nyquist or “folding” frequency) the magnitudes of all frequency
components of signal and noise are reduced to less than the system resolution.
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For 12-bit data acquisition systems with a resolution of 0,05 % the filter attenuation shall be less than 0,05 %
to 2 Hz, and the attenuation shall be greater than 99,95 % at all frequencies greater than one-half the
sampling frequency.
NOTE For a Butterworth filter the attenuation is given by
=
A
2n
⎛⎞f
max
1+
⎜⎟
f
⎝⎠
and
=
A
2n
⎛⎞f
N
1+
⎜⎟
f
⎝⎠0
where
n is the order of the filter;
f is the relevant frequency range (2 Hz);
max
f is the filter cut-off frequency;
f is the Nyquist or “folding” frequency;
N
f is the sampling frequency = 2 × f
s N
For example, for a fourth-order filter:
⎯ for A = 0,999 5, f = 2,37 × f = 4,74 Hz;
0 max
⎯ for A = 0,000 5, f = 2 × (6,69 × f ) = 63,4 Hz.
s
7.3.3.3 Phase shifts and time delays for anti-aliasing filtering
Excessive analog filtering shall be avoided, and all filters shall have sufficiently similar phase characteristics to
ensure that time delay differences lie within the required accuracy for the time measurement.
Phase shifts are especially significant when measured variables are multiplied together to form new variables.
This is because, while amplitudes multiply, phase shifts and associated time delays add. Phase shifts and
time delays are reduced by increasing f . Whenever equations describing the presampling filters are known, it
is practical to remove their phase shifts and time delays by simple algorithms performed in the frequency
domain.
NOTE In the frequency range in which the filter amplitude characteristics remain flat, the phase shift, ϕ, of a
Butterworth filter can be approximated by
ϕ = 81° (f/f ) for 2nd order,
⎯
⎯ ϕ = 150° (f/f ) for 4th order,
⎯ ϕ = 294° (f/f ) for 8th order.
The time delay for all filter orders is t = (ϕ/360°) × (1/f )
7.3.3.4 Data sampling and digitizing
At 2 Hz the signal amplitude changes by up to 1,25 %/ms. To limit dynamic errors caused by changing analog
−6
inputs to 0,1 %, sampling or digitizing time shall be less than 80 × 10 s. All pairs or sets of data samples to
be compared shall be taken simultaneously or over a sufficiently short time period.
In order not to exceed an amplitude error of 0,5 % in the relevant frequency range from zero to f , the
max
sampling rate, f , shall be at least 30 f .
s max
7.3.3.5 Data acquisition system requirements
The data acquisition system shall have a resolution of 12 bits or more (± 0,05 %) and an accuracy of
2 LSB ± 0,1 %. Anti-aliasing filters shall be of order four or higher and the relevant frequency range shall be
from 0 Hz to f .
max
For fourth-order filters, f shall be greater than 2,37 f if phase errors are subsequently adjusted in digital data
0 max
processing, and greater than 5 f otherwise; data sampling frequency f shall be greater than 13,4 f .
max s 0
For filters of orders other than the fourth order, f and f shall be selected for adequate flatness and prevention of
0 s
alias error.
Amplification of the signal before digitizing shall be such that in the digitizing process the additional error is less
−6
than 0,2 %. Sampling and digitizing time for each data channel sampled shall be less than 80 × 10 s.
7.3.3.6 Digital filtering
For filtering of sampled data in data evaluation, phaseless (zero-phase-shift) digital filters shall be used, in
accordance with the following (see Figure 1):
⎯ the passband shall range from 0 Hz to 2 Hz;
⎯ the stopband shall begin at < 6 Hz;
⎯ the filter gain in the passband shall be 1 ± 0,005 (100 ± 0,5) %;
⎯ the filter gain in the stopband shall be u 0,01 (u 1 %);
⎯ the filter gain shall fall within the unshaded area of Figure 1.
6 © ISO 2011 – All rights reserved

X frequency, in Hz
Y filter gain
a
Passband.
b
Stopband.
Figure 1 — Required characteristics of phaseless digital filters
8 Test conditions
8.1 General
Limits and specifications for the ambient wind and vehicle test conditions in accordance with 8.3 and 8.4 shall
be maintained throughout 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).
8.2 Test track
All standard tests shall be carried out on a smooth, clean, dry and uniform paved road surface. The gradient of
the paved surface shall not exceed 2,5 % in any direction when measured over any distance greater than or
equal to the vehicle track. In addition, for tests concerned with damping of combination vehicles, the gradient
of the test surface shall not exceed 1 % along the path of the vehicle as measured over any distance of 25 m
or more. For each test the road surface conditions and paving material shall be recorded in the test report
(see Annex A).
8.3 Weather conditions
During the measurements, ambient wind velocity shall not exceed 5 m/s.
For each test procedure, weather conditions shall be recorded in the test report (see Annex A).
Since, in certain cases, ambient temperature can have a significant influence on test results, it should be
taken into account when making comparisons between vehicles.
8.4 Test vehicle
8.4.1 General data
Appropriate general data on the test vehicle or vehicle unit shall be presented in the test report in accordance
with Annex A.
8.4.2 Tyres
For the standard test conditions, new tyres shall be fitted on the test vehicle according to the vehicle
manufacturer's specifications. They shall have a tread depth of at least 90 % of the original value in the
principal grooves within 0,75 of the tread breadth (in accordance with specifications for tread-wear indicators
given in ECE Regulation No. 30), shall have been stored in accordance with the manufacturer's
recommendation and shall not have been manufactured more than two years prior to the test. The date of
manufacture shall be noted in the test report (see Annex A).
NOTE The tread breadth is the width of that part of the tread which, with the tyre correctly inflated, is in contact with
the road in normal straight-line driving.
If not otherwise specified by the tyre manufacturer, the tyres shall be run in for at least 150 km on the test
vehicle or an equivalent vehicle without excessively harsh use such as severe braking, acceleration, cornering
or hitting the kerb. After running in, the tyres shall be maintained at the same position on the vehicle
throughout the tests.
Tyres shall be inflated to the pressure specified by the vehicle manufacturer for the test vehicle configuration.
The tolerance for setting the cold inflation pressure is ± 2 %.
Inflation pressure and tread depth before tyre warm-up and after completion of the test shall be recorded in
the test report (see Annex A).
The tests may also be performed with tyres in any state of wear as well as with retreaded or regrooved tyres.
The details shall be recorded in the test report (see Annex A). As tread depth or uneven tread wear can have
a significant influence on test results, these should be taken into account when making comparisons between
vehicles or between tyres.
8.4.3 Other operating components
For the standard test conditions, any operating component likely to influence the results of a test (e.g. 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 recorded in the test report
(see Annex A).
Levelling systems of the chassis and cabin suspension which affect the response behaviour inappropriately
should be disabled during steady-state and step-input tests.
8.4.4 Vehicle loading conditions
8.4.4.1 General
The maximum design total mass (Code: ISO-M07) and the maximum design axle load (Code: ISO-M12), in
accordance with ISO 1176:1990, 4.7 and 4.12, shall not be exceeded.
The total weight and the centre-of-gravity position (longitudinal, lateral and vertical) can be expected to
influence all test results. Moments of inertia can be expected to influence transient test results. For all tests,
the total mass and the centre-of-gravity position in three dimensions should be reported for each vehicle unit,
and for transient tests, the moment of inertia in yaw should also be reported. Moments of inertia in pitch and
roll should be reported if available.
8 © ISO 2011 – All rights reserved

Alternatively, the loading condition of the vehicle shall be described adequately such that these parameters
can be reproduced.
Care shall be taken to ensure that the masses, centre-of-gravity positions and moments of inertia of the test
vehicle compare closely to those parameters of the vehicle in normal use. The resulting static wheel loads
shall be determined and recorded in the test report (see Annex A).
8.4.4.2 Minimum loading condition
For the minimum loading condition, the total mass of the vehicle or combination shall consist of the complete
vehicle kerb mass (Code: ISO-M06) in accordance with ISO 1176:1990, 4.6, plus the mass of the
instrumentation. In the case of the first vehicle unit, the mass of the driver and, if applicable, the mass of an
instrument operator or observer shall be added. The minimum loading condition is optional.
8.4.4.3 Maximum loading condition
For the maximum loading condition, the total mass of a fully laden vehicle or combination shall consist of the
complete vehicle kerb mass plus the maximum load of interest (e.g. the legal limit) distributed such that none
of the maximum axle loads is exceeded (see ISO 1176). The height of the centre of gravity and the mass
distribution of the payload should be established to reflect the application of interest. The maximum loading
condition is the standard test condition.
8.4.4.4 Other loading conditions
Other loading conditions, representing special transport conditions, are encouraged.
8.5 Warm-up
All relevant vehicle components shall be warmed up prior to the tests in order to achieve a temperature
representative of normal driving conditions. Tyres shall be warmed up prior to the tests to achieve an
equilibrium temperature and pressure representative of normal driving conditions.
To warm up the tyres, a procedure by driving at the test speed for a distance of at least 50 km or equivalent to
driving 5 km at a lateral acceleration of 1 m/s (left and right turn each) could be appropriate.
The tyre pressures after warm-up may be recorded.
8.6 Test speed
All tests shall be conducted at either 80 km/h, 90 km/h or 100 km/h, depending on the intended use of the
vehicle, or at the maximum speed of the vehicle if it is less than 80 km/h. Other test speeds of interest may be
used (preferably in 10 km/h steps).
For each test run, the average speed shall be maintained 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.
8.7 Lateral acceleration
IMPORTANT — Stepwise increase of the lateral acceleration and the use of outriggers are strongly
recommended in order to prevent rollover.
The lateral acceleration of the vehicle, or first vehicle unit in the case of combinations, shall be appropriate to
the particular type of test. For linear tests, the lateral acceleration of all vehicle units shall be small enough to
generate only linear vehicle behaviour. For nonlinear tests, the lateral acceleration shall be large enough to
have the vehicle show nonlinear behaviour.
The recommended value of the lateral acceleration level should be 3 m/s , except for the random input test
where the lateral acceleration level should be 2 m/s . For safety reasons, the maximum lateral acceleration
should be smaller than 75 % of the estimated rollover limit or 75 % of the road adhesion limit.
The applied lateral acceleration level shall be recorded in the test report (see Annex B).
NOTE Lateral acceleration measured from different vehicles cannot be compared.
8.8 Average longitudinal acceleration
For tests concerned with damping of combination vehicles, the average longitudinal acceleration over the time
period during which measurements are actually made shall be within ± 0,1 m/s .
9 Step input
9.1 Test procedure
Drive the vehicle at the test speed (see 8.6) in a straight line. Starting from a steady-state condition with yaw
velocity in the range of ± 0,5 °/s, apply a steering input as rapidly as possible to a preselected value and
maintain it at that value until the measured vehicle motion variables reach a steady state.
Take data for both left and right turns. All data shall be taken in one direction followed by all data in the other
direction. Alternatively, take data successively in each direction for each acceleration level, from the lowest to
the highest level. Record the method chosen in the test report (see Annex A).
Data shall be taken throughout the desired range of steering inputs and response variable outputs.
Increase the steering-wheel amplitude stepwise up to a magnitude sufficient to produce the desired lateral
acceleration level (see 8.7).
Perform at least three test runs at each steering-wheel angle amplitude.
9.2 Data analysis
9.2.1 Response time
The transient-response data reduction shall be carried out such that the origin for each response is the time at
which the steering-wheel angle change is 50 % complete. This is the reference point from which all response
times are measured. Response time is thus defined as the time, measured from this reference, for the vehicle
transient response to first attain the designated percentage of its new steady-state value. The 90 % response
times should be determined (see Figure 2), and in some cases it may be desirable to determine other
response times, for example, the 63 % response time.
9.2.2 Peak response time
The peak response time is the time, measured from the reference point, for a vehicle transient response to
reach its peak value (see Figure 2).
In some instances, system damping can be so high that a peak value cannot be determined. If this occurs,
data sheets should be marked accordingly.
9.2.3 Overshoot values
The overshoot values are calculated as a ratio: the difference of peak value minus steady-state value divided
by steady-state value.
10 © ISO 2011 – All rights reserved

Key
X time 3 steady state
1 steering-wheel input 4 90 % steady state
2 vehicle motion response 5 50 % level
a
Response time.
b
Peak response time.
Figure 2 — Response time and peak response time
9.3 Data presentation
9.3.1 General
General data shall be presented in accordance with Annex A.
9.3.2 Time histories
The time histories of variables used in data reduction shall be plotted. If a curve is fitted to any set of data, the
method of curve fitting shall be described in the presentation of results in accordance with Annex B.
Plot the time histories of steering-wheel angle, lateral accelerations and yaw velocities for the selected lateral
acceleration level, as shown in Figure B.1.
9.3.3 Time-response data summary
Record in accordance with Table B.1, as applicable, the means and standard deviation of the following
variables for the selected test speed and the lateral acceleration level:
⎛⎞
ψ
a) steady-state yaw velocity response gain, ;
⎜⎟
δ
⎝⎠H
ss
⎛⎞
a
Y
b) steady-state lateral acceleration response gain, ;
⎜⎟
δ
⎝⎠H
ss
c) lateral acceleration response time, T ;
aY
d) yaw velocity response time, T ;
ψ
e) lateral acceleration peak response time, T ;
aY,max
f) yaw velocity peak response time, T ;
ψ,max
g) overshoot value (see 9.2.3) of lateral acceleration, U ;
aY
h) overshoot value (see 9.2.3) of yaw velocity, U .
ψ
The confidence intervals for these variables should also be determined.
10 Sinusoidal input — One period (see ISO/TR 8725)
10.1 Test procedure
Drive the vehicle at the test speed (see 8.6) in a straight line. Starting from a steady-state condition with yaw
velocity in the range of ± 0,5 °/s, apply one full period sinusoidal steering-wheel input with a frequency of
0,2 Hz. An additional frequency of 0,5 Hz should also be used. The amplitude error of the actual waveform
compared to the true sine wave shall be less than 5 % of the first peak value.
Take data while the steering wheel is rotated initially both to the left and to the right. All data may be taken in
one direction followed by all data in the other direction. Alternatively, take data successively in each direction
for each acceleration level, from the lowest to the highest level. Record the method chosen in the test report
(see Annex A).
Increase the steering-wheel amplitude stepwise up to a magnitude sufficient to produce the desired lateral
acceleration level (see 8.7 and 10.2.2).
Perform at least three test runs for each combination of speed and steering.
10.2 Data analysis
10.2.1 General
The test results can be sensitive to the method of data processing. The procedure given in ISO/TR 8725
should therefore be used.
10.2.2 Lateral acceleration
Lateral acceleration in this test is defined as the first peak value of the lateral-acceleration time history.
10.2.3 Yaw velocity
Yaw velocity in this test is defined as the first peak value of the yaw-velocity time history.
10.2.4 Time lags
The time lags between the variables steering-wheel angle and lateral acceleration and yaw velocity are
calculated for the first and second peaks by means of cross-correlation of the first and second half-waves,
respectively (positive and negative parts of the time history).
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10.2.5 Lateral acceleration gain
Lateral acceleration gain shall be calculated as the ratio of the lateral acceleration (in accordance with 10.2.2)
to the corresponding peak value of the steering-wheel angle.
10.2.6 Yaw velocity gain
Yaw velocity gain shall be calculated as the ratio of the yaw velocity (according to 10.2.3) to the corresponding
peak value of the steering-wheel angle.
10.3 Data presentation
10.3.1 General
General data shall be presented in accordance with Annex A.
10.3.2 Time histories
Time histories of variables used in data reduction shall be plotted. If a curve is fitted to any set of data, the
method of curve fitting shall be described in the presentation of results (see Annex B).
Plot the time histories of steering-wheel angle, lateral accelerations and yaw velocities for the selected lateral
acceleration level as shown in Figure B.2.
10.3.3 Time-response data summary
Test data shall be presented in summary form as presented in Table B.2, as mean values ± standard
deviation (see 10.1).
The confidence intervals for the appropriate variables should also be determined.
10.3.4 Data as functions of lateral acceleration
If optional measurements are made at other lateral accelerations, it is useful to present data as functions of
lateral acceleration. The justification for making two initial turn directions is that an asymmetry can exist. This
asymmetry can be presented in terms of asymmetry factors. These further types of presentation are described
in detail in ISO/TR 8725.
11 Random input (see ISO/TR 8726)
11.1 Test procedure
Make the test runs by driving the vehicle at the selected test speed (see 8.6) while making continuous inputs
to the steering wheel up to predetermined limits of steering-wheel angle.
The test shall cover a minimum frequency range of 0,1 Hz to 2 Hz. Optionally, the frequency range may also
be extended above and below these limits.
Do not use mechanical limiters of steering-wheel angle, owing to their effect on the harmonic content of the
input. It is also important that the input be continuous, as periods of relative inactivity will seriously reduce the
signal-to-noise ratio.
To ensure adequate high-frequency content, the input should be energetic (see 11.2.2 and 11.2.3).
To ensure enough total data, capture at least 12 min of data, unless confidence limits indicate that a shorter
time is sufficient. Ideally, this should be accomplished in a continuous run, but practical considerations can
prevent this for two reasons. Firstly, the test track could be insufficiently long to permit a continuous run of
such length at the required test speed. Secondly, the computer used to analyse the data might not be large
enough to handle all the data at once. In either case, data may be captured using a number of shorter runs of
at least 30 s duration.
Determine the steering-wheel angle limits by steady-state driving on a circle, the radius of which gives the
desired steady-state lateral acceleration (see 8.7) at the selected test speed (see 8.6). The recommended
steady-state lateral acceleration is 2 m/s or less, as necessary to remain within the range in which the vehicle
exhibits linear properties (see “IMPORTANT” in Clause 4, and ISO/TR 8726). Optionally, higher lateral
accelerations may also be used, provided the vehicle remains in the linear range.
11.2 Data analysis
11.2.1 General
The data processing can be carried out using a multi-channel real-time analyser or a computer with the
appropriate software (see ISO/TR 8726).
11.2.2 Preliminary analysis
A spectral analysis shall be made of the steering-wheel angle time history. The result shall be displayed as a
graph of the input level versus frequency, as shown in Figure B.3.
This graph shall be examined to ensure adequate frequency content. The recommended ratio between
maximum and minimum steering-wheel angle should not be greater than 4:1. If this ratio is greater, the results
may be discarded or, if used, the extent of the ratio shall be recorded in the test report (see Figure B.3).
11.2.3 Further data processing
The data shall then be processed using appropriate equipment to produce the transfer function amplitude and
phase information together with the coherence function for the following combinations of input and output
variables:
⎯ lateral acceleration related to steering-wheel angle;
⎯ yaw velocity related to steering-wheel angle.
If data have not been captured in a continuous run, calculate the auto and cross-spectral de
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