GB/T 44126.2-2024 PDF English
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Road vehicles - Test of braking systems on vehicles with a maximum authorized total mass of over 3.5 t using a roller brake tester - Part 2: Air over hydraulic and purely hydraulic braking systems
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GB/T 44126.2-2024: Road vehicles - Test of braking systems on vehicles with a maximum authorized total mass of over 3.5 t using a roller brake tester - Part 2: Air over hydraulic and purely hydraulic braking systems
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GB
NATIONAL STANDARD OF THE
PEOPLE'S REPUBLIC OF CHINA
ICS 43.040.40
CCS T 24
Road vehicles - Test of braking systems on vehicles with a
maximum authorized total mass of over 3.5 t using a roller
brake tester - Part 2.Air over hydraulic and purely
hydraulic braking systems
(ISO 21069-2.2008, MOD)
Issued on: MAY 28, 2024
Implemented on: SEPTEMBER 1, 2024
Issued by. State Administration for Market Regulation;
Standardization Administration of PRC.
Table of Contents
Foreword... 3
Introduction... 5
1 Scope... 6
2 Normative references... 6
3 Terms and definitions... 6
4 Symbols... 7
5 Test conditions and measurement methods... 8
Appendix A (Normative) Technical requirements for roller brake tester... 13
Foreword
This document was drafted in accordance with the provisions of GB/T 1.1-2020
Directives for standardization - Part 1.Rules for the structure and drafting of
standardizing documents.
This document is part 2 of GB/T 44126 Road vehicles - Test of braking systems on
vehicles with a maximum authorized total mass of over 3.5 t using a roller brake tester.
GB/T 44126 has been published in the following parts.
-- Part 2.Air over hydraulic and purely hydraulic braking systems.
This document is modified in relation to ISO 21069-2.2008 Road vehicles - Test of
braking systems on vehicles with a maximum authorized total mass of over 3.5 t using
a roller brake tester - Part 2.Air over hydraulic and purely hydraulic braking systems.
This document has made the following structural adjustments compared to ISO 21069-
2.2008.
-- Chapter 2 is added;
-- Chapter 3 corresponds to Chapter 2 of ISO 21069-2.2008;
-- Chapter 4 corresponds to Chapter 3 of ISO 21069-2.2008;
-- Chapter 5 corresponds to Chapter 4 of ISO21069-2.2008.
The technical differences between this document and ISO 21069-2.2008 and their
reasons are as follows.
-- The scope of application of the standard is changed to clarify the content of the
standard (see Chapter 1);
-- The normative reference GB/T 15089 is added to clarify the specific vehicle
models to which it is applicable (see Chapter 1).
The following editorial changes were made to this document.
-- Appendix B of ISO 21069-2.2008 has been deleted because it does not contain
specific technical content;
-- Note 2 of 4.4.2 in ISO 21069-2.2008 has been deleted because this part does not
contain specific technical content.
Please note that some of the contents of this document may involve patents. The issuing
organization of this document does not assume the responsibility for identifying patents.
Road vehicles - Test of braking systems on vehicles with a
maximum authorized total mass of over 3.5 t using a roller
brake tester - Part 2.Air over hydraulic and purely
hydraulic braking systems
1 Scope
This document specifies the terms and definitions, test methods, test conditions, test
equipment, and data processing for the test of brake systems using a roller brake tester.
This document is applicable to tests on vehicles of categories M2, M3, N2, N3, O3 and
O4 as specified in GB/T 15089, with a maximum authorized total mass of more than
3.5 t and equipped with air-over-hydraulic and purely hydraulic brake systems using a
roller tester.
2 Normative references
The provisions of the following documents constitute the essential clauses of this
document through normative references in this text. Among them, for referenced
documents with dates, only the versions corresponding to the dates are applicable to
this document; for referenced documents without dates, the latest versions (including
all amendments) are applicable to this document.
GB/T 15089 Classification of power-driven vehicles and trailers
3 Terms and definitions
The following terms and definitions apply to this document.
3.1 braking force
The force generated between the tire tread and the rotating drum during braking, that is,
the reaction force generated by the roller brake tester to cause the wheel to rotate.
3.2 braking force imbalance
The difference in braking force between the left and right wheels on the same axle.
NOTE. The braking force imbalance is expressed as a percentage of the braking force value on the larger
side.
3.3 braking force variation
The difference between the maximum and minimum braking force of the single-side
wheels measured under constant driving force.
NOTE. The braking force variation is expressed as a percentage of the larger braking force value on one
side.
3.4 roller brake tester
The testing equipment that is composed of two pairs of left and right power-driven
rollers and is used to test the braking performance of vehicles.
NOTE. The axle wheels are driven and supported by rollers, and the braking force between the single
wheel/double wheels and the driving roller is measured and evaluated simultaneously or separately.
4 Symbols
See Table 1 for general symbols and definitions, and Table 2 for special symbols and
definitions for air-over-hydraulic braking systems.
5 Test conditions and measurement methods
5.1 General
The characteristics of the roller brake tester shall comply with the provisions of
Appendix A.
The braking system performance test shall be carried out as follows.
-- regulatory requirements;
-- data provided by the vehicle manufacturer;
-- instructions for the roller brake tester.
5.2 Vehicle and roller brake tester preparation
5.2.1 Clean the vehicle tires and adjust the tire pressure according to the vehicle
manufacturer's recommendations.
5.2.2 For the motor vehicle brake test required by the nation, the brake tester shall be
kept clean, the inspector shall be certified by the technical service department, and the
static axle load shall be measured using additional equipment when the tester is not in
operation. After the test, the vehicle information and measurement values shall be
recorded.
5.3 Test data calculation and evaluation
5.3.1 Calculation of braking strength
5.3.1.1 Overview
For air-over-hydraulic and purely hydraulic braking systems, connecting the measuring
device increases the risk of leakage when measuring the hydraulic system. Therefore,
it is particularly important not to use additional pressure sensors for the calculation of
the braking strength.
If the braking force increases predictably with increasing pressure, the brake test is
performed under full or partial load conditions.
5.3.1.2 Air-over-hydraulic braking system
The schematic diagram of the air-over-hydraulic braking system is shown in Figure 1.
For the front axle, an air pressure measuring device is installed before the air-over-
hydraulic converter. The output hydraulic pressure is calculated on the basis of the
measured air pressure and the air-over-hydraulic conversion coefficient according to
formula (1). Other similar calculation methods can also be used.
For the rear axle, the influence of the load-sensing valve needs to be considered. The
load-sensing valve characteristics are given in the form of a graph or table, that is, the
load-sensing proportional coefficient between the pressure output and the axle load
input is expressed, and the output hydraulic pressure is calculated according to formula
(2).
In the above cases, the axle load is known or measured.
The calculated pHF and pHR can be used as pAi to be put into formula (5) and formula
(6).
The calculation of the braking output force can be used to predict the full-load braking
strength, which can be achieved by the following two-point measurement method. To
ensure the accuracy of the data (pressure-braking force), the interval between the first
measuring point (starting point) and the second measuring point (end point) is as large
as possible.
NOTE. If there are relevant national regulations, measure the roller rotation resistance according to the
regulations.
Appendix A
(Normative)
Technical requirements for roller brake tester
A.1 Technical features
A.1.1 Based on the maximum rated axle load, the roller brake tester can be divided into
many types, and the maximum rated axle load can reach 13000 kg. Considering the
detection capability under full load, the maximum rated axle load state sets the
maximum braking force measurement range. The details are as follows.
-- Maximum axle load is m (in kilograms), acceleration of gravity is g=10 m/s2,
then the vertical load on one side of the wheel is mg/2 (in Newtons).
-- Under the condition of dry adhesion coefficient μ=0.7, the braking force of the
single-sided roller is μmg/2=0.35mg.
A.1.2 The roller diameter shall not be less than 200 mm. The roller diameter of the
ground-type roller brake tester shall not be less than 150 mm.
A.1.3 The length of each roller shall not be less than 900 mm.
A.1.4 The distance between the rollers shall ensure that vehicles with tire diameters of
530 mm~1300 mm can be tested.
A.1.5 In order to obtain the locking point of the tested axle under greater braking
force/wheel end pressure, the height of the upper surface of the roller can be raised to
40 mm, but not higher than the front roller by 100 mm.
In order to inspect the multi-axle group (bogie), some rollers shall be raised. The upper
surface of the rear roller and the front roller can be raised by 40 mm, but the height
from the ground shall not be greater than 100 mm.
A.1.6 When the tires normally used on commercial vehicles are used for testing, the
surface adhesion coefficient of the driving roller shall be above 0.7 in dry state and
above 0.5 in wet state.
NOTE. Due to the distance between the two rollers, the effective adhesion coefficient may be lower than
the above values.
A.1.7 The test equipment shall be able to operate at an ambient temperature of at least
5 °C~40 °C (can be lower than 5 °C). If it is necessary to operate at a temperature
outside this range, the local ambient temperature shall be controlled or a tester designed
for more extreme conditions shall be used.
A.1.8 The installation and use of roller brake test equipment shall comply with national
workplace safety standards. In the absence of such standards, the following minimum
requirements apply.
a) If the test device is equipped with an automatic roller start function, the roller
can only start after the axle is placed on the roller for 3 seconds or more.
b) An automatic cut-off function shall be provided to avoid tire damage. If the
slip between the tire and the roller is detected to be beyond the range of
27%±3%, the test shall be terminated automatically.
c) The roller drive shall stop automatically once the vehicle axle leaves the roller
tester.
d) It shall have a safety function to ensure that the two pairs of rollers can only
be started when the left and right wheels of the tested vehicle are loaded
simultaneously.
e) The working foundation pit where the roller brake tester is installed shall be
equipped with a foundation pit safety system.
f) If installed on a foundation pit, the roller brake tester shall have an automatic
stop function. When someone enters the dangerous area in the pit (the entire
pit length or within 2.5 m from the roller in any direction), the roller drive shall
stop.
g) It shall have an emergency stop function, and its button shall be located in a
conspicuous position.
h) It shall have a protection function to ensure that electrical/electronic control
and transmission are free from electromagnetic interference and any other
interference.
i) There shall be measures to prevent the roller drive motor from starting
accidentally.
A.2 Measurement system range and resolution
A.2.1 Measurement range
The measurement range of single-wheel braking force shall be calculated according to
A.1.1.Table A.1 lists several common axle loads and their corresponding maximum
design braking forces.
......
Source: Above contents are excerpted from the full-copy PDF -- translated/reviewed by: www.ChineseStandard.net / Wayne Zheng et al.
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