Standards related to:

GB/T 12538-2023**GB/T 12538-2023: PDF in English (GBT 12538-2023) **

GB/T 12538-2023

GB

NATIONAL STANDARD OF THE

PEOPLE’S REPUBLIC OF CHINA

ICS 43.020

CCS T 40

Replacing GB/T 12538-2003

Road Vehicles - Determination of Center of Gravity

(ISO 10392:2011, MOD)

ISSUED ON: NOVEMBER 27, 2023

IMPLEMENTED ON: JUNE 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 ... 5

2 Normative References ... 5

3 Terms and Definitions ... 5

4 Measurement Preparation and Preliminary Measurement ... 5

5 Determination of Horizontal Center of Gravity ... 8

6 Determination of Height of Center of Gravity ... 9

Appendix A (informative) Comparison Table of Structural No... 21

Appendix B (informative) Table of Technical Differences and Causes ... 23

Appendix C (informative) Test Record of Axle lift Method ... 25

Appendix D (informative) Test Record of Stable Pendulum Method ... 28

Appendix E (informative) Test Record of Tilt-table Method ... 31

Bibliography ... 35

Road Vehicles - Determination of Center of Gravity

1 Scope

This document specifies a method for the determination of center of gravity of road vehicles

and describes a method for the determination of horizontal center of gravity and three methods

for the determination of the height of center of gravity.

This document is applicable to motor vehicles, trailers and combination vehicles. The axle lift

method for the measurement of the height of center of gravity is not applicable to articulated

passenger cars, semi-trailers, drawbar trailers (the drawbar has a supporting function), center-

axle trailers and combination vehicles.

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 3730.3 Motor Vehicles and Towed Vehicles - Dimensions of Vehicles - Terms and

Definitions (GB/T 3730.3-1992, ISO 612:1978, NEQ)

GB/T 12549 Terms and Definitions for Vehicle Controllability and Stability (GB/T 12549-2013,

ISO 8855:1991, NEQ)

GB/T 12673 Motor Vehicle Main Dimensions Measurement Method

GB/T 12674 Motor Vehicles - Weight Parameter - Measuring Method

3 Terms and Definitions

The terms and definitions defined in GB/T 3730.1, GB/T 3730.3 and GB/T 12549 are applicable

to this document.

4 Measurement Preparation and Preliminary Measurement

4.1 Coordinate System

Adopt the vehicle coordinate system specified in GB/T 12549, that is, the positive x direction

points forward along the main movement direction of the vehicle, the positive y direction points

horizontally to the left, and the positive z direction points upward.

4.2 Vehicle Preparation

4.2.1 Stowage

The load status of the vehicle shall be determined in accordance with the measurement

demands. The measurement of the unloaded center of gravity shall be based on the complete

vehicle kerb mass status. If it is necessary to load simulated loads, all loads shall be reliably

fixed.

The fuel tank of a fuel vehicle must be filled to at least 90% of the manufacturer’s design

capacity (it should be filled to the full). The impact of the significant shift of the oil level during

the measurement on the measurement result of the center of gravity shall be taken into

consideration.

4.2.2 Seat

The longitudinal and vertical position of the seat shall be adjusted in accordance with the

vehicle manufacture’s requirements, and the seat back angle shall be adjusted (for seats with

corresponding adjustment functions).

4.2.3 Tire

Under the test load condition, the cold inflation pressure of the tire of the test vehicle shall

comply with the vehicle manufacturer’s stipulations.

4.2.4 Suspension

The suspension should be locked in accordance with the normal working position required by

the vehicle manufacturer, and other flexibly installed vehicle components can also be locked.

For height-adjustable suspensions, the height adjustment function shall be in the OFF state, or

the suspension mode / position specified by the manufacturer.

4.2.5 Transmission and brake

On the premise of ensuring the safety of the vehicle, the transmission shall be placed in the

neutral position, and the automatic transmission shall be placed in the N gear; the parking brake

shall be released.

When using the stable pendulum method for measurement, the transmission shall be placed in

the P position and the parking brake shall be activated.

4.2.6 Other requirements

During the entire process of measuring the center of gravity, the vehicle power system is in a

non-working state, the windows are closed, and the wheels are traveling in a straight line.

Figure 2 -- Side View of Measurement of Height of Vehicle’s Center of Gravity Using the

Stable Pendulum Method

For the unstable pendulum method, a similar model and equilibrium equation can be used,

except that the rotation axis is lower than the position of the center of gravity of the system

composed of the vehicle and the vehicle supporting platform. For the unstable pendulum

method, static braking torque is required to maintain the stability of the vehicle / platform

system at any given tilt angle relative to the rotation axis. Under this circumstance,

measurements using a scale or weighing cell placed at a known distance from the rotation axis

can be used to determine the torque required to balance the system. In accordance with the

formulas in this document, similar formulas for the unstable pendulum method can be derived,

but the mathematical signs of some terms may need to be changed. By requiring the same

accuracy level for the required measuring instruments and equipment instructions, the final

accuracy of the unstable pendulum method can be basically the same as that of the stable

pendulum method.

The placement of the front and rear restraint components of the vehicle is shown in Figure 2.

When determining mp and hp, it is necessary to use the total mass (mres) of the restraint

components and the height of center of gravity (hres) of the restraint components.

6.2.2 Vehicle fixing and mechanical components

Weigh the prepared vehicle and record its total mass (mv), then, the vehicle shall be restrained

on the platform in a mode that minimizes the movement of the chassis relative to the platform.

The total mass (mres) of the restraint components (gaskets, blocks, jacks and straps, etc.) and the

height of center of gravity (hres) of the mass of the restraint components shall be determined and

recorded.

The platform structure shall be stiff enough to support the test vehicle without generating

significant vertical deformation. In addition, the bearings of the rotation axis shall be low-

friction and precisely aligned.

The distance in the height direction of the rotation axis from the platform (hpivot) and the position

of the applied load (lA and hA) shall be accurately measured.

6.2.3 Measurement procedures

6.2.3.1 Park a vehicle that complies with the measurement conditions on a stable pendulum

platform, so that the position of the vehicle’s center of gravity and the position of the platform’s

center of gravity are aligned as closely as possible in the longitudinal direction, and at the same

time, the longitudinal center of gravity of the vehicle / platform system is almost directly under

the rotation axis. At the beginning of the test, the tilt angle between the restraint vehicle and the

platform shall be less than 0.5. Measure and record the initial tilt angle of the platform (ZERO).

6.2.3.2 The accuracy of the calculation of the height of center of gravity relies on accurate

measurement of the initial offset (x) between the vehicle’s center of gravity and the platform’s

center of gravity in the longitudinal direction of the vehicle. Measure and record the initial

system through the load mA. The calculation formula is shown in Formula (13):

Where,

g---acceleration of gravity, expressed in (m/s2).

6.2.6 Impact of platform deformation

The platform used for measurement must have sufficient strength. However, even a very rigid

platform may deform under vehicle loads. Platform deformation changes the position of the

vehicle’s center of gravity relative to the rotation axis. Utilizing the relationships between wheel

load, wheelbase and axle track, the vertical deformation of the platform under the action of the

vehicle can be theoretically calculated, which is represented here by Dz. Dz is the average

deformation of the vehicle tire due to the mass of the vehicle. The amount of platform

deformation is a function of the geometric construction of a specific platform.

For rigid platforms, platform deformation is not important for most test vehicles. However, for

integrity, it shall be included in the data analysis for all test vehicles.

The height of center of gravity of the platform will also very due to the mass of the vehicle, and

this change in the height of center of gravity of the platform is similar to Dz in magnitude.

The change in the height of center of gravity of the platform (hp) due to vehicle mass can also

be calculated based on vehicle wheelbase, vehicle mass, platform length and other platform-

specific parameters. The height of center of gravity of the platform is corrected in accordance

with Formula (14):

6.2.7 Position of height of center of gravity

The distance (hv) between the vehicle’s center of gravity and the platform’s rotation axis is

calculated by summing the moments acting on the rotation axis (see Figure 2). The calculation

formulas are shown in Formula (15) and Formula (16):

Where,

∑Mpivot---the moment acting on the rotation axis, expressed in (N m).

be adopted as much as possible.

The tilt angle during the measurement has a direct impact on the results. If the angle is too

small, the mass transfer is not obvious, and the measurement accuracy is not high; if the angle

is too large, the mass transfer is relatively large, and the deformation of the tires may affect the

measurement result. Therefore, the tilt angle cannot be too large or too small.

6.3.2 Environmental conditions

During the measurement, the ambient wind speed shall not be greater than 5 m/s, and the lateral

wind speed shall not be greater than 3 m/s.

6.3.3 Measurement procedures

6.3.3.1 After measuring the wheelbase and axle track of the vehicle, drive the vehicle straight

onto the tilt-table; park the vehicle at a suitable position as required, turn off the vehicle’s power

system, and measure the wheel load while the vehicle is in a level condition.

6.3.3.2 The test bench shall gradually tilt [the maximum rising speed (uniform speed) is not

greater than 3/min]. Record the tilt angle and corresponding wheel load. It is recommended to

record data from at least 5 angles.

NOTE: during the measurement, the tilt angle () range is selected from 6 ~ 12 for more accurate

measurement results.

6.3.3.3 Use the formulas provided in 6.3.4 to calculate the height of center of gravity of each

set of data, then, average these values to obtain the data of the height of center of gravity.

6.3.3.4 Drive the vehicle away from the plane of the tilt-table, then, park the vehicle being

measured on the tilt-table as required. In accordance with the stipulations of 6.3.3.2 and 6.3.3.3,

continue the measurement and calculation, with a total of 3 measurements. The height of center

of gravity of unilateral tilt is the arithmetic mean of 3 measurement results.

6.3.3.5 Turn the vehicle’s head direction and park it on the tilt-table. Then, tilt it to the other

side and perform the same measurement.

6.3.3.6 The height of center of gravity of the vehicle is the arithmetic mean of the height of

center of gravity tilted to the left and the height of center of gravity tilted to the right.

6.3.4 Position of height of center of gravity

When tilting to the left (the observer and the vehicle are in the same direction) at angle , the

height of center of gravity (zCG), expressed in (mm), is calculated in accordance with Formula

(19):

......

Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.