GB/T 44124-2024 PDF English
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GB/T 44124-2024: Road load determination of road vehicles---This is an excerpt. Full copy of true-PDF in English version (including equations, symbols, images, flow-chart, tables, and figures etc.), auto-downloaded/delivered in 9 seconds, can be purchased online: https://www.ChineseStandard.net/PDF.aspx/GBT44124-2024
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 43.020
CCS T 04
Road Load Determination of Road Vehicles
(ISO 10521-1.2006, Road Vehicles - Road Load - Part 1.Determination under
Reference Atmospheric Conditions, MOD)
Issued on: MAY 28, 2024
Implemented on: SEPTEMBER 1, 2024
Issued by. State Administration for Market Regulation;
Standardization Administration of the People’s Republic of China.
Table of Contents
Foreword... 3
1 Scope... 4
2 Normative References... 4
3 Terms and Definitions... 4
4 Requirements for Instruments and Equipment... 6
5 Road Load Measurement on the Road... 7
6 Road Load Measured by Wind Tunnel and Dynamometer... 27
Appendix A (informative) Comparison of Structural No... 39
Appendix B (informative) Table of Technical Differences and Causes... 44
Appendix C (informative) Onboard Anemometer Calibration Procedures... 47
Appendix D (informative) Vehicle Information Sheet... 51
Road Load Determination of Road Vehicles
1 Scope
This document describes the method for road test determination of road load and the methods
for wind tunnel and chassis dynamometer determination.
This document is applicable to Category-N1 vehicles, as well as Category-M1 and Category-M2
vehicles below 3,500 kg.
2 Normative References
The contents of the following documents constitute indispensable clauses of this document
through the normative references in the text. In terms of references with a specified date, only
versions with a specified date are applicable to this document. In terms of references without a
specified date, the latest version (including all the modifications) is applicable to this document.
GB/T 3730.1 Terms and Definitions of Motor Vehicles, Trailers and Combination Vehicle - Part
1.Types
GB/T 3730.2 Road Vehicle - Masses - Vocabulary and Codes
GB 18352.6-2016 Limits and Measurement Methods for Emissions from Light-duty Vehicles
(CHINA 6)
3 Terms and Definitions
The terms and definitions defined in GB/T 3730.1, GB/T 3730.2 and GB 18352.6-2016, and
the following are applicable to this document.
3.1 road load
The resistance to the movement of a vehicle measured by the coasting method or an equivalent
method.
NOTE. it includes the frictional resistance of the transmission system.
3.2 running resistance
The resistance torque opposite to the running direction of a vehicle measured by a torque meter
installed on the driving wheels of the vehicle.
NOTE. road load refers to road load or running resistance.
3.3 aerodynamic drag
A force generated by the air that is opposite to the running direction of a vehicle.
3.4 rolling resistance
A force on the tires that is opposite to the running direction of a vehicle.
3.5 reference speed
A vehicle running speed used to determine road load or chassis dynamometer load.
3.6 reference atmospheric conditions
Unified atmospheric conditions, which are specified as follows.
a) Atmospheric pressure. p0 = 100 kPa;
b) Atmospheric temperature. T0 = 20 C;
c) Dry air density. 0 = 1.189 kg/m3;
d) Wind speed. 0 m/s.
3.7 stationary anemometry
On a test road that can represent the wind speed conditions, use an anemometer for the
measurement of wind speed and direction.
3.8 onboard anemometry
Use an anemometer mounted on the test vehicle, measure the wind speed and direction.
3.9 wind correction
In stationary anemometry or onboard anemometry, correct the effect of wind speed on road load.
3.10 aerodynamic stagnation point
When the airflow surrounding an object and the relative motion of the object are divided into
flows in two or more directions, the airflow diverging point.
3.11 test mass
The sum of the reference mass of the test vehicle, the mass of optional equipment and the mass
of representative load.
NOTE 1.the reference mass refers to the curb weight of the test vehicle, plus 100 kg.
NOTE 2.the mass of optional equipment refers to the mass of other selected optional equipment
combinations, in addition to the standard vehicle equipment specified by the
manufacturer’s technical conditions.
If it is impossible to conduct the test in both forward and backward directions on the same test
road (for example, only one-way traffic is allowed on an oval test road), wind speed and
direction shall be measured on each part of the test road. At this moment, the type of
anemometer used shall be determined based on the higher measured wind speed, and whether
the wind correction can be exempted shall be determined based on the lower measured wind
speed.
5.1.1.2 Atmospheric temperature
During the test, the atmospheric temperature shall be between 5 C ~ 40 C.
If the temperature difference between the maximum temperature and minimum temperature
measured during the coasting test is greater than 5 C, each coasting shall be individually
corrected based on the arithmetic mean of the temperatures measured during the test. At this
moment, each coasting shall be separately calculated, and the road load coefficient shall be
individually corrected. The final road load coefficient shall be calculated based on the
arithmetic mean of the above-mentioned individual corrections.
The test may be carried out within the temperature range of 1 C ~ 5 C in accordance with the
requirements of the vehicle manufacturer.
5.1.2 Test road
The test road surface shall be flat, clean, dry and hard, with a texture and composition
representative of current typical urban roads and highway pavements, with no obstructions or
wind barriers that may impede road load measurement.
The longitudinal gradient of the test road shall not exceed 1%.
The gradient difference between any 3 m on the test road shall not exceed 0.5%. If the two-
way coasting test cannot be carried out on the same toad (for example, oval test road that only
allows one-way traffic), then, the sum of the longitudinal gradients of the parallel test sections
shall be within the range of 0% ~ 0.1%, and the maximum arc of the test road shall be not
greater than 1.5%.
5.2 Preparation of Test Road
5.2.1 Vehicle preparation
5.2.1.1 Vehicle status
The test vehicle shall be properly driven and the tires shall be run-in in accordance with the test
demands. The tread depth of the test vehicle shall not be lower than 50% of the initial tread
depth.
The test vehicle shall be in normal conditions specified by the manufacturer or be set up in
accordance with the purpose of the test. There shall be no atypical friction resistance in the tire
pressure, wheel alignment, body height, lubricants in the transmission system and wheel
shall not exceed the maximum reference speed.
5.3 Road Load Determined Using Coasting Method
5.3.1 Multi-section method
5.3.1.1 Selection of speed points
At least four speed points shall be selected, vj (j = 1, 2, 3, 4, etc.) to obtain the road load curve
based on vehicle speed. The maximum speed point shall not be lower than the maximum
reference speed, and the minimum speed point shall not be higher than the minimum reference
speed.
The reference speed shall start from 20 km/h and increase in steps of 10 km/h. The maximum
reference speed shall be determined based on the following provisions.
a) The maximum reference speed shall be 130 km/h, which can be adjusted to 120 km/h
for pure electric vehicles. The determination of road load and the setting of chassis
dynamometer shall be performed at the same reference speed point.
b) If the maximum reference speed plus 14 km/h is greater than or equal to the maximum
speed of the test vehicle, when determining the road load or setting the resistance on
the chassis dynamometer, this speed shall be eliminated. At this moment, the next
highest reference speed becomes the maximum reference speed of the vehicle.
5.3.1.2 Data collection
During the test, the following data shall be collected, in which, a) and b) shall be measured and
recorded at a maximum interval of 0.2 s, and c) and d) shall be measured and recorded at a
maximum interval of 1.0 s.
a) Time it takes;
b) Vehicle speed;
c) Wind speed;
d) Wind direction.
NOTE. the wind speed and direction shall be measured through the stationary anemometry.
5.3.1.3 Vehicle coasting
5.3.1.3.1 After pre-treatment, before each test, if necessary, the vehicle may be driven at the
maximum reference speed for up to 1 minute. Then, accelerate the vehicle to a speed 5 km/h
higher than the speed (vj + v) measured at the beginning of coasting (v is the speed change),
and immediately start coasting.
5.3.1.3.2 During coasting, the transmission shall be in the neutral gear and the engine shall be
5.4.2 Data collection
During the test, the following data shall be measured and recorded at a maximum interval of
0.2 s.
a) Time it takes;
b) Vehicle speed;
c) Wind speed and direction.
NOTE. the wind speed and direction shall be measured through the onboard anemometry.
5.4.3 Vehicle coasting
In accordance with the provisions of 5.3.1.3.1 ~ 5.3.1.3.4, after installing an onboard
anemometer on the vehicle, carry out vehicle coasting. The installation position of the
anemometer shall minimize the impact on the vehicle’s operating characteristics. Choose any
of the following modes to install the onboard anemometer.
a) About 2 m in front of the vehicle’s front aerodynamic stagnation point;
b) At the center line of the roof, if possible, install the onboard anemometer within 30
cm above the windshield;
c) At the center line of the vehicle’s engine hood, at the midpoint of the line connecting
the front of the vehicle and the bottom of the windshield.
No matter which mode is adopted, it shall be ensured that the installed anemometer is parallel
to the road surface. If the installation mode b) or c) is adopted, the additional aerodynamic
effects generated by the anemometer shall be corrected. Through the wind tunnel test, coasting
can be performed with or without an onboard anemometer installed on the vehicle (the
installation position of the onboard anemometer is consistent with the road test). In accordance
with the test results, calculate the changes in aerodynamic drag characteristics with or without
the onboard anemometer, as well as the vehicle’s orthographic projection area, and correct the
coasting test results.
Before conducting the coasting test, the onboard anemometer shall be calibrated in accordance
with the manufacturer's specifications. Appendix C provides an example of the calibration of
onboard anemometer.
5.4.4 Coefficient determination
Utilize the coasting time and wind data, in accordance with the formula of multiple regression
analysis provided in Formula (34), calculate each coefficient.
6.1.3.1 The test vehicle shall be placed parallel to the longitudinal centerline of the wind tunnel,
and the maximum deviation from the centerline shall not exceed 10 mm. The test vehicle shall
be placed at a yaw angle of 0, with the maximum deviation not exceeding 0.1.
6.1.3.2 The engine hood / cover and all windows shall be closed, any covers of the ventilation
system and headlights, etc. shall be closed, and the fresh air switching device of the air
conditioning system shall be turned off. The test vehicle shall be fixed in a mode that minimizes
the impact on airflow.
6.1.3.3 In accordance with wind tunnel laboratory specifications, conduct the measurement.
During the test, it is recommended that the vehicle body posture be as consistent as possible
with the actual road condition. Under the following wind speed conditions, measure the
aerodynamic drag at two wind speeds.
a) Type-1 vehicles.
1) Low wind speed vlow. vlow 80 km/h;
2) High wind speed vhigh. vlow + 40 km/h vhigh 150 km/h.
b) Type-2 and Type-3 vehicles.
1) Low wind speed vlow. 80 km/h vlow 100 km/h;
2) High wind speed vhigh. vlow + 40 km/h vhigh 150 km/h.
Among them.
The ratio Pmr of the rated power of Type-1 vehicles to the vehicle mass in running order
minus 75 kg is not greater than 22 W/kg.
The ratio Pmr of the rated power of Type-2 vehicles to the vehicle mass in running order
minus 75 kg is greater than 22 W/kg, but not greater than 34 W/kg.
The ratio Pmr of the rated power of Type-3 vehicles to the vehicle mass in running order
minus 75 kg is greater than 34 W/kg.
6.1.3.4 The measurement time of aerodynamic drag shall not be less than 60 s, and the
measurement frequency shall not be lower than 5 Hz. If the lowest frequency is 1 Hz, the
measurement shall be continuously carried out for at least 300 seconds, and the test result shall
be the arithmetic mean of the test data. Two measurements shall be carried out, and if the
deviation between the two measured CDA values is greater than 1%, then, the test vehicle and
wind tunnel settings shall be checked and corrected, and two more measurements shall be
carried out. Repeat this process, until the deviation between the two values does not exceed 1%.
6.1.3.5 If the test vehicle has adjustable body parts, which are related to the vehicle speed, the
aerodynamic characteristics of the adjustable parts at different positions shall be measured in
the wind tunnel, and data and materials on the relations among the reference speed and the
positions of the adjustable parts and CDA shall be submitted (such as. rear spoiler, active air
intake grille, air suspension, etc.).
6.1.4 Test result
By averaging the two measurement values, determine the test result CDA, which is expressed in
(m2).
6.2 Determination of Rolling Resistance with a Chassis Dynamometer
6.2.1 Test device
6.2.1.1 Chassis dynamometer
Both the front and rear axles are equipped with single drums with a diameter of not less than
1.2 m. The force measured in the X direction includes the friction loss of the transmission
system.
6.2.1.2 Vehicle restraint system
6.2.1.2.1 Alignment system
The dynamometer shall be equipped with an alignment system. During the coasting test to
determine the road load, the restraint system shall ensure that the alignment accuracy of the
driving wheel position is within the specified limits.
6.2.1.2.2 Vehicle position
The test vehicle shall be horizontally placed and safely fastened to the chassis dynamometer.
6.2.1.2.3 Vertical force
The vehicle restraint system shall not add additional restraining force in the vertical direction
of the vehicle.
6.2.1.3 Force measurement accuracy
Only the force required to turn the wheel shall be measured. External forces (such as. cooling
fan force, vehicle restraint force, flat-belt aerodynamic force and dynamometer losses, etc.)
shall not be introduced into the test results.
The measurement accuracy of the X direction force shall reach 5 N.
6.2.1.4 Dynamometer speed control
The rolling speed control deviation shall be within 0.2 km/h.
6.2.1.5 Drum surface
6.2.2.2 Test procedures at steady vehicle speed
6.2.2.2.1 The test shall start from the maximum reference speed and end at the minimum
reference speed.
6.2.2.2.2 After the measurement of the previous reference speed point is completed, there shall
be a smooth transition to the next reference speed point, and the deceleration shall not exceed
1 m/s2.
6.2.2.2.3 The stabilization time at the reference speed point is 4 s ~ 10 s, and the signal of the
test equipment shall be stable.
6.2.2.2.4 At each reference speed point, force measurement shall be performed continuously
for no less than 6 seconds. During the measurement, the vehicle speed remains constant, and
the force FjDyno obtained at the reference speed point shall be the arithmetic mean during the
measurement.
6.2.2.2.5 For each reference speed point, repeat the measurement steps of 6.2.2.2.2 ~ 6.2.2.2.4.
6.2.2.3 Measurement procedures under deceleration
6.2.2.3.1 In accordance with 6.2.2.1, carry out the pre-treatment and dynamometer settings.
Before each coasting test, the test vehicle shall run at the maximum reference speed or 110%
of the maximum reference speed, for no less than 1 minute. Then, raise the vehicle speed to a
speed at least 10 km/h higher than the maximum reference speed, and start coasting.
6.2.2.3.2 During the coasting process, the gearbox shall be the in neutral gear, steering wheel
rotation shall be avoided as much as possible, and do not perform braking operation. Each
coasting shall be continuously carried out. If the data of all reference speed points cannot be
continuously recorded, the coasting can also be carried out in sections. When coasting in
sections, it shall be noted that the vehicle status shall remain unchanged. If the deviation of the
force measured in two consecutive coasting tests is within 10 N, then, the coasting test is over.
6.2.2.3.3 In accordance with Formula (69), calculate the force at each reference speed.
Where,
FjDecel---the force Fj at the reference speed point j calculated in accordance with 5.3.1.4.4,
expressed in (N);
cd---the aerodynamic drag coefficient, expressed in [N/(km/h)2].
At the manufacturer’s request, when determining FjDyno during the coasting test, cd can be
set to 0.
road load coasting test, the centerline of the test vehicle’s driving wheels satisfies the following
requirements.
a) The transverse direction of the test vehicle shall be kept consistent with the Y-axis, so
as to minimize transverse movement;
b) On the basis that the test vehicle is consistent with the Y-axis direction, the deviation
between the front and rear axles and the transverse centerline of the flat belt shall be
within 10 mm;
c) The vehicle restraint system shall not add additional restraining force in the vertical
direction of the vehicle.
6.3.1.3 Force measurement accuracy
Only the force required to turn the wheel shall be measured. External forces (such as. cooling
fan force, vehicle restraint force, flat-belt aerodynamic force and dynamometer losses, etc.)
shall not be introduced into the test results.
The measurement accuracy of force in the X direction shall reach 5 N.
6.3.1.4 Flat-belt speed control
The flat-belt speed control accuracy shall reach 0.1 km/h.
6.3.1.5 Flat-belt surface
The flat-belt surface shall be clean, dry, and free of substances that can make the tires slip.
6.3.1.6 Cooling
A variable-speed fan shall be used to cool the test vehicle, and the airflow speed at the fan outlet
shall be 5 km/h higher than the corresponding measurement speed of the dynamometer. The
deviation of the airflow speed at the fan outlet and the corresponding speed of the dynamometer
shall be within 5 km/h, or 10%, whichever is greater.
6.3.2 Flat-belt measurement
The measurement procedures shall comply with the provisions of 6.2.2.
6.3.3 Measurement result of flat-belt method
The measurement result FjDyno of flat-belt dynamometer may be used for the subsequent
calculation of Fj in 6.4.
6.4 Road Load Calculation
6.4.1 Correction of flat-belt and chassis dynamometer test results
Appendix C
(informative)
Onboard Anemometer Calibration Procedures
C.1 Principle
Based on the requirements for the coasting method of onboard anemometer, an instrument that
measures the apparent relative air speed and apparent yaw angle encountered by the vehicle
during the coasting test. The method described below requires calibration data collection
assuming minimal changes in true wind speed and true wind attack angle during each pair of
opposite direction drives.
C.2 Instruments and Theory
The meteorological anemometer is installed on the mast, about 2 m in front of the vehicle, at
about the aerodynamic stagnation height, and flush with the front bumper of the vehicle.
Typically, this device generates an anemometer-propeller rotation signal proportional to the
apparent relative air speed, as well as a static signal indicating the angular orientation of the
anemometer blades relative to a certain reference location. Assuming that these signals are
correlated with the observed changes in vehicle deceleration, hence, in the aerodynamic drag
(Faero) formula described in 5.4.4, the coefficients S, a0, a1, a2, a3 and a4 can be determined, as
shown in Formula (C.1).
The “zero yaw offset” shall be calculated through the method described in this Appendix. It is
impossible that the aerodynamic centerline of the anemometer and the aerodynamic centerline
of the vehicle are exactly the same.
The following procedure outlines the method, in which, the anemometer signals can be
correlated with vehicle deceleration.
C.3 Assumptions and Procedural Recommendations
C.3.1 Symbols
The symbols in C.3 and their meanings are as follows.
v---the vehicle speed, expressed in (km/h);
va---the apparent air speed in the running direction of the vehicle, regardless of wind force,
expressed in (km/h);
......
Source: Above contents are excerpted from the full-copy PDF -- translated/reviewed by: www.ChineseStandard.net / Wayne Zheng et al.
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