Agricultural tractors -- Test procedures

This document specifies a method of determining the position of the centre of gravity of agricultural tractors. The method is applicable to agricultural tractors having at least two axles fitted with wheels or tracks.

Tracteurs agricoles -- Méthodes d'essai

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Status
Published
Publication Date
04-Feb-2019
Current Stage
6060 - International Standard published
Start Date
26-Dec-2018
Completion Date
05-Feb-2019
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INTERNATIONAL ISO
STANDARD 789-6
Second edition
2019-02
Agricultural tractors — Test
procedures —
Part 6:
Centre of gravity
Tracteurs agricoles — Méthodes d'essai —
Partie 6: Centre de gravité
Reference number
ISO 789-6:2019(E)
ISO 2019
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ISO 789-6:2019(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2019

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
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Phone: +41 22 749 01 11
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Email: copyright@iso.org
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Published in Switzerland
ii © ISO 2019 – All rights reserved
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ISO 789-6:2019(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Apparatus ..................................................................................................................................................................................................................... 2

5 General requirements ..................................................................................................................................................................................... 2

6 Procedure..................................................................................................................................................................................................................... 3

6.1 General principle ................................................................................................................................................................................... 3

6.2 Determination of horizontal fore-and-aft coordinate ( x ) ................................................................................ 3

6.2.1 Tracked tractors [see Figure 1 a)] ................................................................................................................... 3

6.2.2 Wheeled tractors [see Figure 1 b)] ................................................................................................................. 3

6.3 Determination of vertical coordinate ( h ) (see Figure 2) ................................................................................. 3

6.4 Determination of lateral coordinate in the horizontal plane ( y ) (see Figure 3) ........................ 4

7 Test report ................................................................................................................................................................................................................22

Annex A (informative) Example calculation: Height of centre of gravity, h (Table 2) ...................................23

Bibliography .............................................................................................................................................................................................................................26

© ISO 2019 – All rights reserved iii
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ISO 789-6:2019(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.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).

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. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso

.org/iso/foreword .html.

This document was prepared by Technical Committee ISO/TC 23, Tractors and machinery for agriculture

and forestry, Subcommittee SC 2, Common tests.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www .iso .org/members .html.

This second edition cancels and replaces the first edition (ISO 789-6:1982), which has been technically

revised. It also incorporates the Amendment ISO 789-6:1982/Amd.1:1996. The main changes compared

to the previous edition are as follows.
— The terms and definitions have been updated to reference ISO 789-13.
— A requirement for a mass in the driver’s seat has been added in 5.2.
— A requirement for locking the suspension has been added in 5.4.

— A new method has been added for alternative determination of vertical coordinate ( h) in 6.3.8.

— Figures 4 to 12 and Tables 1 to 4 have been added to support the method described in 6.3.8.

A list of all parts in the ISO 789 series can be found on the ISO website.
iv © ISO 2019 – All rights reserved
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ISO 789-6:2019(E)
Introduction

This document specifies test procedures for agricultural tractors. It deals with the centre of gravity.

Although there are many possible methods of determining the centre of gravity, the purpose of this

document is to specify a simple, practical method, which requires the use of a weighbridge and crane.

Alternative methods can be used if they locate the centre of gravity with respect to the specified

reference planes and within the specified tolerances.
© ISO 2019 – All rights reserved v
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INTERNATIONAL STANDARD ISO 789-6:2019(E)
Agricultural tractors — Test procedures —
Part 6:
Centre of gravity
1 Scope

This document specifies a method of determining the position of the centre of gravity of agricultural

tractors.

The method is applicable to agricultural tractors having at least two axles fitted with wheels or tracks.

2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements 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 789-13:2018, Agricultural tractors — Test procedures — Part 13: Vocabulary and specimen test report

3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 789-13 and the following apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
agricultural tractor

self-propelled agricultural vehicle having at least two axles and wheels, or endless tracks, particularly

designed to pull agricultural trailers and to pull, push, carry and operate implements used for

agricultural work (including forestry work), which may be provided with detachable loading platform

Note 1 to entry: The agricultural vehicle has a maximum design speed of not less than 6 km/h and may be

equipped with one or more seats.
[SOURCE: ISO 12934:2013, 3.1]
3.2
wheelbase

horizontal distance between the two vertical planes passing through the rotational centrelines of the

wheels, where one plane is for the front wheels and the other for the rear wheels

Note 1 to entry: In the case of a tractor equipped with a rear tandem, it is the distance between two vertical

planes passing through the centres of the front wheel and the vertical plane midway between the wheel centres

of the two axles of the tandem.
[SOURCE: ISO 789-13, 3.2, modified]
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ISO 789-6:2019(E)
4 Apparatus
The following apparatus are required.
4.1 Weighbridge or load cells.
4.2 Crane.
4.3 Decking with knife edges.
4.4 Level.
4.5 Plumb rule.
4.6 Squares.

4.7 Scribing board, shall be at least 600 mm high by 450 mm wide, rigidly constructed, and attached

to the tractor in a suitable position with a smooth face vertical and parallel to the side or other

appropriate plane.
4.8 Marking materials.
4.9 Tape measure.
5 General requirements

5.1 The tractor shall be clean and shall be tested in normal working conditions or in a specified

condition agreed between the manufacturer and the testing authority.

5.2 The radiator, sump, hydraulic and other reservoirs shall be filled to specified working levels. The

fuel tank shall be full and the driver replaced by a weight of 75 kg on the driver’s seat, the tractor being

otherwise unballasted.

5.3 Tools, spare tyre, and loose accessories and equipment shall be complete as supplied and shall be

in the normal storage positions.

5.4 Any suspension system shall be locked in the normal height position. If locking the suspension

system is not possible, then inflate all tires up to the maximum permissible pressure as specified by the

tyre manufacturer. The difference in radius of the wheels on the fixed axle between horizontal and raised

position shall not be higher than 1,5 % of the wheel radius.

5.5 Articulated tractors shall normally be tested locked in a straight line, but it may be necessary to

conduct the test with the joint set at the maximum or any intermediate angle.

5.6 If testing a sprung tractor, no special measures shall be taken to lock the suspension of the machine.

5.7 In conducting the test, the following measurement tolerances shall be observed:

a) distance: ±0,5 %;
b) mass: ±0,5 %;
2 © ISO 2019 – All rights reserved
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ISO 789-6:2019(E)
c) tyre pressure: ±5 %.
Tyre pressure should be in accordance with the manufacturer’s recommendations.
6 Procedure
6.1 General principle

The centre of gravity is determined by the suspension and ground reaction method. This involves

measuring the ground reactions with the tractor:
a) in a horizontal position;
b) tilted with one end lifted;
c) tilted with the other end lifted.

The calculated horizontal distance of the centre of gravity from a ground contact point is measured in

each case and verticals are drawn on the scribing board (4.7) fixed to the tractor. The intersection of

the verticals indicates the centre of gravity.
6.2 Determination of horizontal fore-and-aft coordinate ( x)
6.2.1 Tracked tractors [see Figure 1 a)]
Determine the mass (m) of the whole tractor on the weighbridge.

Measure the reaction (F ) under the knife edge due to its mass and part of the decking.

Move the tractor on to the decking, part supported by the weighbridge, and measure the reaction at

the front knife edge due to the mass of the tractor, the decking and knife edge (F + F ). Calculate the

1 2

reaction of the front knife edge due to the tractor mass only (F ) by subtraction.

Measure the distance (d) between the knife edges.
The horizontal fore-and-aft coordinate is given by Formula (1):
dF⋅
x = (1)
6.2.2 Wheeled tractors [see Figure 1 b)]

In the case of wheeled tractors, it is not necessary to use decking or knife edges. With the brakes off,

measure the axle loads and calculate x from the mass and the wheelbase of the tractor using Formula (1)

(using the wheelbase as the value for d).
6.3 Determination of vertical coordinate ( h) (see Figure 2)

6.3.1 Suspend the tractor from one end at an angle of 20° to 25° to the horizontal, the other end resting

on the weighbridge. For some tractors, it may not be practical or safe to use an angle this large. In this

case, a lesser angle may be used but shall not be less than 15° to the horizontal. (The method is applicable

either to wheeled or tracked tractors, the main difference being in establishing the exact location of the

point of application of the ground contact. In the case of wheeled tractors, which shall be unbraked, this

is vertically below the axle. In the case of tracked tractors, it is necessary to manoeuvre until the contact

grousers are in the line of ground contact BB’ on either side, or to make contact through a knife-edge on

the ground contact line BB’. In all cases, the suspension cable shall be vertical as tested by plumb rule.)

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ISO 789-6:2019(E)
6.3.2 Measure the reaction (F ) at the ground contact on the weighbridge.

6.3.3 Measure the horizontal distance (d) from the ground contact to the line of suspension.

6.3.4 Calculate the horizontal distance (c) from the centre of gravity to the line of suspension using

Formula (2):
Fd⋅
c = (2)
where m is the mass of the tractor.

6.3.5 Draw a vertical line on the scribing board at a distance c from the line of suspension.

6.3.6 Repeat the procedures specified in 6.3.1 to 6.3.5 with the tractor suspended from the other end.

The suspension angle need not be the same for both ends.

6.3.7 The intersection of the two lines on the scribing board, determined as specified in 6.3.5 and 6.3.6,

gives the vertical coordinate of the centre of gravity ( h).

NOTE 1 The tractor can be conveniently run on to the weighbridge, square, using chalked lines. This will assist

in drawing the plan. If, in the case of tracked tractors, the grousers are not in the ground contact line BB’ (see

Figure 2), the tractor can be driven in varying circles until the required result is attained at the last approach.

NOTE 2 An alternative method is to use a tilting platform and load cells respectively.

6.3.8 Alternative determination of vertical coordinate ( h) (See Figures 4 to12).

Repeat the procedures specified in 6.3.1 to 6.3.4 with the tractor suspended from the other end. The

suspension angle need not be the same for both ends.

Vertical coordinate ( h) of the centre of gravity is determined by means of calculation (see Tables 1, 2,

3 and 4)

NOTE The tractor can be conveniently run on to the weighbridge, square, using chalked lines. This will assist

in drawing the plan. If, in the case of tracked tractors, the grousers are not in the ground contact line BB’ (see

Figure 2), the tractor can be driven in varying circles until the required result is attained at the last approach..

6.4 Determination of lateral coordinate in the horizontal plane ( y) (see Figure 3)

Measure the left-hand (F ) and right-hand (F ) wheel or track loadings. Calculate the offset (b) of the

4 5

centre of gravity using track gauge or wheel track (d ) as the moment arm, i.e. Formula (3):

b= (3)
The lateral coordinate in the horizontal plane is given by the Formula (4);
y=−b (4)

NOTE The right-hand and left-hand side loads usually do not exactly total the mass of the tractor due to

small differences in level between the weighbridge deck and the surround. Any error is minimized by equalizing

the overlap of the side being weighed in both case
...

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