ISO 4138:2004
(Main)Passenger cars — Steady-state circular driving behaviour — Open-loop test methods
Passenger cars — Steady-state circular driving behaviour — Open-loop test methods
ISO 4138:2004 specifies open-loop test methods for determining the steady-state circular driving behaviour of passenger cars as defined in ISO 3833 and light trucks.
Voitures particulières — Tenue de route en régime permanent sur trajectoire circulaire — Méthodes d'essai en boucle ouverte
General Information
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Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 4138
Third edition
2004-09-15
Passenger cars — Steady-state circular
driving behaviour — Open-loop test
methods
Voitures particulières — Tenue de route en régime permanent sur
trajectoire circulaire — Méthodes d'essai en boucle ouverte
Reference number
ISO 4138:2004(E)
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ISO 4138:2004(E)
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ISO 4138:2004(E)
Contents Page
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
4.1 Test methods . 1
4.2 Equivalence of test methods . 2
5 Variables . 2
5.1 Reference system . 2
5.2 Measurement . 2
6 Measuring equipment . 3
6.1 Description . 3
6.2 Transducer installation . 3
6.3 Data processing . 3
7 Test conditions . 3
8 Test procedure . 3
8.1 Warm-up . 3
8.2 Initial driving condition . 4
8.3 General test description . 4
8.4 Method 1 — Constant-radius . 4
8.5 Method 2 — Constant steering-wheel angle . 5
8.6 Method 3 — Constant-speed . 6
9 Data analysis . 6
9.1 General . 6
9.2 Lateral acceleration . 7
9.3 Path radius . 7
10 Data evaluation and presentation of results . 7
10.1 General . 7
10.2 Plotted results (see Annex A) . 7
10.3 Evaluation of characteristic values . 8
Annex A (normative) Presentation of results . 12
Annex B (normative) Determination of overall (static) steering ratio . 17
Annex C (informative) General information — Theoretical basis for the test methods . 18
Bibliography . 19
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ISO 4138:2004(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 4138 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 4138:1996), which has been technically revised.
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ISO 4138:2004(E)
Introduction
The dynamic behaviour of a road vehicle is a most important part of active vehicle safety. Any given vehicle,
together with its driver and the prevailing environment, forms a unique closed-loop system. The task of
evaluating dynamic behaviour is therefore very difficult since there is a significant interaction between these
driver-vehicle-environment elements, each of which is complex in itself. A complete and accurate description of
the behaviour of the road vehicle must necessarily involve information obtained from a number of tests of
different types. Since they quantify only a 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 effort 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. Therefore, it is not possible to use these methods and test results for regulatory
purposes.
Finally, test conditions and tyres have a strong influence on test results. Only vehicle dynamic properties
obtained under identical test and tyre conditions are comparable.
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.
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INTERNATIONAL STANDARD ISO 4138:2004(E)
Passenger cars — Steady-state circular driving behaviour —
Open-loop test methods
1Scope
This International Standard specifies open-loop test methods for determining the steady-state circular driving
behaviour of passenger cars as defined in ISO 3833 and of light trucks, such behaviour being one of the factors
comprising vehicle dynamics and road-holding properties. The open-loop manoeuvres included in these
methods are not representative of real driving conditions, but are nevertheless useful for obtaining measures of
vehicle steady-state behaviour resulting from several specific types of control inputs under closely controlled
test conditions.
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 3833:1977, Road vehicles — Types — Terms and definitions
ISO 7401:2003, Road vehicles — Lateral transient response test methods — Open-loop test methods
ISO 8855:1991, Road vehicles — Vehicle dynamics and road-holding ability — Vocabulary
ISO 15037-1:1998, Road vehicles — Vehicle dynamics test methods — Part1: General conditions for
passenger cars
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 8855 and the following apply.
3.1
low-speed path radius
radius of the circular path transcribed by the origin of the vehicle axis system when the vehicle is operated at
constant speed with a given fixed steering-wheel angle and with approximately zero lateral acceleration
4 Principle
4.1 Test methods
Three test methods are specified:
— Method 1, the constant-radius test method;
— Method 2, the constant steering-wheel angle test method;
— Method 3, the constant-speed test method.
Each method is presented with two variations and differs in requirements for testing space, driver skill, and
instrumentation. Methods1 and 3 depend upon the path-keeping ability of the driver to minimize
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instrumentation requirements. Method 2 uses fixed steering-wheel angle and calculates path radius from
measures of inertial instruments.
4.2 Equivalence of test methods
The nature of any stable steady state is independent of the method by which it is achieved. Therefore, to obtain
a desired set of steady-state equilibrium conditions of speed, steering-wheel angle and turn radius, it is possible
to hold any one of them constant, vary a second and measure the third. Thus, a constant-radius test method (in
which speed is varied and steering-wheel angle is measured), a constant steering-wheel angle test method (in
which speed is varied and radius is calculated from variables of vehicle motion) or a constant-speed test
method (in which radius is varied and steering-wheel angle is either measured or varied and the radius
calculated from variables of vehicle motion) may be used. The conditions that are to be held constant, varied
and measured or calculated are summarized in Table 1.
Table 1 — Test conditions
Measured or
Test method Constant Varied
calculated
Constant radius Radius Speed Steering-wheel angle
Constant steering-wheel angle Steering-wheel angle Speed Radius
Constant speed with discrete turn radii Speed Radius Steering-wheel angle
Constant speed with discrete steering-wheel
Speed Steering-wheel angle Radius
angles
All three test methods will produce equivalent steady-state results, provided they span the same combination of
speed-steer-radius steady-state conditions. Moreover, in principle, an equivalent to any of the methods can be
obtained by cross-plotting a series of results from one to produce the results from another.
EXAMPLE Taking points at constant speed from a series of constant-radius tests run on different turn radii.
In practice, however, results obtained from tests conducted with different combinations of speed, steer and
radius may differ due to differences in road-load throttle, aerodynamics, tyre slip and inclination angles at
different steering angles, etc. Also, the steering system is non-linear in many vehicles and does not have a fixed
overall steering ratio. Gradients obtained using one method at a given steady-state equilibrium condition can
differ from those obtained using another because, while in one method lateral acceleration is controlled by
changing speed, in another it is controlled by changing the steering-wheel angle. Practical considerations such
as tyre heating during long test runs and failure to maintain true steady state also tend to affect test results.
5 Variables
5.1 Reference system
The provisions given in ISO 15037-1:1998, 3.1, apply.
5.2 Measurement
Measure the following variables:
a) longitudinal velocity (v );
X
b) lateral acceleration (a );
Y
c) steering-wheel angle (δ ).
H
Alternatively, lateral acceleration may be determined from other motion variables (see 9.2).
NOTE The method chosen to determine lateral acceleration could require the measurement of additional variables (yaw
velocity, vehicle roll angle, or sideslip angle) for use in the computation.
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The following variables should also be measured:
— yaw velocity (dψ/dt);
— sideslip angle (βv) and/or lateral velocity ( );
Y
— longitudinal acceleration (a );
X
— vehicle roll angle (ϕ );
V
— steering-wheel torque (M ).
H
In addition, front steer angle (δ ) and rear steer angle (δ ) may be measured.
F R
6 Measuring equipment
6.1 Description
The variables selected for test purposes shall be measured using appropriate transducers and the data
recorded on a multi-channel recording system having a time base. Typical operating ranges, and recommended
maximum errors of the transducer and recording system, are given in ISO 15037-1 and Table 2.
Table 2 — Variables, their typical operating ranges and recommended maximum errors
Recommended maximum error of the combined
Variable Typical operating range
transducer/recorder system
◦ ◦
Front steer angle ± 20 ± 0,2
◦ ◦
Rear steer angle ± 10 ± 0,1
Steering-wheel torque ± 30 N· m ± 0,3 N· m
NOTE Increased measurement accuracy could be desirable for computation of some of the characteristic values given in
10.3.
6.2 Transducer installation
The transducer installation shall comply with ISO 15037-1:1998, 4.2.
6.3 Data processing
The provisions given in ISO 15037-1:1998, 4.3 apply.
7 Test conditions
Test conditions shall be in accordance with ISO 15037-1:1998, Clause 5. General data on the test vehicle shall
be recorded as specified in ISO 15037-1:1998, 5.4.1 and the following paragraph.
The tyre type, tyre brand, any special equipment on the test vehicle, any deviation in type or operating condition
of components from the manufacturer's specification, the odometer reading at the beginning and end of the test,
and any other condition that may affect test results shall also be recorded on the test report for general data
(see ISO 15037-1:1998, Annex A).
8 Test procedure
8.1 Warm-up
The warm-up shall be carried out in accordance with ISO 15037-1:1998, 6.1.
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8.2 Initial driving condition
The conditions shall be in accordance with ISO 15037-1:1998, 6.2.1 and 6.2.3, and the following (8.3 to 8.6),
according to which of the three methods and their variations is used.
8.3 General test description
All necessary variables shall be recorded throughout the manoeuvre. Data shall be taken for both left and right
turns.
For tests utilizing discrete increments of speed, radius or steering-wheel angle, all of the test data may be taken
in one turn direction followed by all the data in the other turn direction, as experience has shown that this
minimizes data scatter. However, to obtain more even tyre wear and reduced tyre heating, data may be taken in
alternating turn directions at each test speed/radius/steering-wheel angle.
The method chosen shall be noted in the section for test method specific data on the test report for test
conditions (see ISO 15037-1:1998, Annex B). At a minimum, data shall be taken at increments of lateral
2
acceleration no larger than 0,5 m/s .
NOTE Where data vary rapidly with changes in lateral acceleration, it can be useful to decrease the speed/radius/steering-
wheel angle increments.
The test should be repeated several times so that the results can be examined for repeatability and averaged.
Caution should be exercised during testing so that tyre heating is minimized as much as possible. Tyre heating
is a particular concern for test methods using continuous speed increase, with attendant long periods of data
acquisition, and for all test methods at high levels of lateral acceleration. The tyres should be cooled to normal
operating temperatures between test runs.
8.4 Method 1 — Constant-radius
8.4.1 Description
This test method requires driving the test vehicle at several speeds over a circular path of known radius. 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 directional-control response characteristics are determined from data obtained while driving the vehicle at
successively higher speeds on the constant-radius path. This procedure can be conducted in a relatively small
area. The procedure can be adapted to existing test track facilities by selecting a circle or a path of appropriate
radius. Often a constant-radius (in plane) road will suffice for a test facility.
The constant-radius test exists in two variations. In the first, the vehicle is driven on the circular path at discrete
constant speeds. Data are taken when steady state is attained. The test can be run on any level constant-radius
path of sufficient length to attain and hold on-radius steady state for at least a 3s measurement period. In the
second, the vehicle remains on the circle with a continuous, slow speed increase, during which data are taken.
8.4.2 Procedure
8.4.2.1 General
First, drive the vehicle on the desired circular path at the lowest possible speed. Record data with the steering-
wheel and throttle positions fixed, so that the approximate Ackermann steer angle can be recorded.
Then, drive the vehicle at the next speed at which data are to be taken. Increase the level of the lateral
acceleration and take data until it is no longer possible to maintain steady-state conditions.
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8.4.2.2 With discrete test speeds
Drive the vehicle onto the circle at each test speed. After attaining steady state, in which the desired path radius
is held within ± 0,5 m, the steering wheel and throttle positions shall be held constant for at least 3s.
8.4.2.3 With continuous speed increase
Steadily increase the speed and record data continuously, for as long as the vehicle remains on the desired
2
circular path within ± 0,5 m. The maximum rate of increase of lateral acceleration should be 0,1 m/s /s. The
2
maximum permissible rate of increase of lateral acceleration shall be 0,2 m/s /s.
8.5 Method 2 — Constant steering-wheel angle
8.5.1 Description
This test method requires driving the test vehicle at several speeds with a single selected steering-wheel angle
that is held fixed. The path radius is determined by computation: from horizontal velocity and yaw velocity, or
from horizontal velocity and lateral acceleration. The test exists in two variations: a series of discrete test runs,
or a single continuous test run. In the first, the steering-wheel angle is applied with the vehicle travelling at
discrete speeds and is maintained until steady-state conditions are reached. In the second, the steering-wheel
angle is held fixed while speed is increased continuously at a slow rate, up to the limit of control.
The standard steering-wheel angle shall provide a low-speed path radius of 30 m. Other radii may be used, with
20 m as the minimum. For testing to the limit of control with the standard initial condition, the path radius can
increase to 100 m or more.
8.5.2 Procedure
8.5.2.1 General
First, drive the vehicle at the lowest possible speed to establish the steering-wheel angle for the selected low-
speed path radius.
Then, drive the vehicle at successively higher speeds, with the steering-wheel angle held constant or
◦
mechanically fixed within ± 1 of the selected steering-wheel angle. Run the test through the desired range of
lateral acceleration, or until the limits of test space, vehicle speed, or vehicle stability are reached.
8.5.2.2 With discrete test speeds
At each selected speed, the steering wheel shall be turned to the preselected steering-wheel angle and
maintained until steady-state conditions, including speed and throttle, are attained. The steering-wheel angle
and throttle position shall be held constant for at least 3s.
NOTE This procedure is the same as that of 8.5.2.3, except that the steering-wheel angle is maintained and speed varied.
8.5.2.3 With continuous speed increase
The steering-wheel angle shall be held constant or mechanically fixed at the pre-selected steering-wheel angle
while the vehicle speed is steadily increased. The maximum rate of increase of lateral acceleration should be
2 2
0,1 m/s /s. The maximum permissible rate of increase of lateral acceleration shall be 0,2 m/s /s.
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8.6 Method 3 — Constant-speed
8.6.1 Description
This test method requires driving the test vehicle at one speed on circular paths of different radii, utilizing a
range of steering-wheel angles. The directional-control response characteristics are determined from data
plotted against lateral acceleration. This test method could require large test areas, depending on the
combination of speed and lateral acceleration. The discrete turn radii method requires a number of marked
2
circles or circular segments with different radii, sufficient in number to provide 0,5 m/s lateral acceleration
increments at the selected speed. An adjustable steering stop should be used, for maintaining constant
steering-wheel angles in the discrete steering-wheel angle method.
The standard test speed is 100 km/h. If higher or lower speeds are selected, they shall be in 20 km/h
increments.
8.6.2 Procedure
8.6.2.1 General
From an initial constant-speed driving condition, apply steering inputs of successively increasing magnitude and
◦
± 1 3s
hold them constant or mechanically fixed within for after the measured vehicle motion variables reach
steady state. Control the throttle in order to maintain constant speed within 3% throughout the test run. Run the
test through the desired range of lateral acceleration, or until the limits of test space, vehicle speed, or vehicle
stability are reached.
8.6.2.2 With discrete turn radii
Drive the vehicle onto the circle at the pre-selected speed. After attaining steady state, the steering wheel and
throttle position shall be held constant for at least 3s.
8.6.2.3 With discrete steering-wheel angles
With the vehicle being driven at the pre-selected speed, apply a steering input and hold it constant for at least
3s after the measured vehicle motion variables reach steady state. Control the throttle in order to maintain
constant speed throughout the run.
NOTE It is possible to use the constant-speed test method with discrete steering-wheel angles to extract transient
response measures comparable to those obtained from the step input method of ISO 7401:2003, if the steering input is
applied in accordance with ISO 7401:2003, 8.1. However, since ISO 7401:2003, 8.1, requires a fixed throttle position versus
the controlled throttle position in the constant-speed test method, the resulting transient response measured might not be
identical to those obtained from ISO 7401:2003, 8.2.
9 Data analysis
9.1 General
The steady-state values for all measured variables shall be established as their average values during any time
interval of 1s to 3s during which steady state is maintained. For each selected time interval, the limitations on
path radius, steer angle, speed, rate of increase of lateral acceleration and/or throttle position specified in the
description of the test procedure being followed shall be observed. In addition, for each selected time interval,
the standard deviation of lateral acceleration shall not exceed 5% of its mean value.
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9.2 Lateral acceleration
Theoretically, steady-state characteristics should be determined as functions of centripetal acceleration, which
is measured perpendicular to the path. Traditionally, these characteristics have been expressed as functions of
lateral acceleration, which is measured perpendicular to the intermediate X-axis. At steady state, lateral
acceleration and centripetal acceleration differ only by the cosine of the sideslip angle. In most cases, the
vehicle sideslip angle is small, so lateral acceleration may generally be considered to be equal to centripetal
acceleration. Where large values of vehicle sideslip angle are observed, or where greater accuracy is desired,
centripetal acceleration may be corrected to obtain lateral acceleration.
Steady-state centripetal acceleration may be obtained by any one of the following three methods.
a) The product of yaw velocity and horizontal velocity:
dψ
×v
h
dt
b) The square of the horizontal velocity, divided by the path radius:
2
v
h
R
c) The product of the square of the yaw velocity and the path radius:
� �
2
dψ
×R
dt
The method used to determine lateral acceleration shall be noted in the test report.
9.3 Path radius
For the constant steering-wheel angle test method, path radius R (see ISO8855:1991, 2.3.2) may be
computed at steady state from longitudinal velocity, corrected for sideslip angle, divided by yaw velocity,
corrected for vehicle roll angle.
10 Data evaluation and presentation of results
10.1 General
General data on the test vehicle shall be presented on a summary form using the general data test report
contained in ISO 15037-1:1998, Annex A. The general test conditions shall be presented using the test
conditions test report contained in ISO 15037-1:1998, Annex B.
10.2 Plotted results (see Annex A)
Measured data shall be plotted directly against lateral acceleration on figures, as follows:
a) steering-wheel angle data points for the constant-radius and constant-speed test methods on Figure A.1;
b) path radius data points for the constant steering-wheel angle test method on Figure A.2;
c) sideslip angle data points, if measured, on Figure A.3;
d) vehicle roll angle data points, if measured, on Figure A.4;
e) steering-wheel torque data points, if measured, on Figure A.5.
Curves may be fitted to the plotted points either freehand or by one of the many mathematical routines
available. The method of curve fitting should be stated. This is particularly recommended where the process
involves fitting smooth curves to experimental data for the purpose of evaluating the gradients. The type of
curve and the method of fitting will influence the results obtained.
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NOTE Within the context of an International Standard, it is not possible to recommend any one way as being better than
another.
10.3 Evaluation of characteristic values
...
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