ISO 7641:2012

INTERNATIONAL ISO
STANDARD 7641
First edition
2012-11-15
Road vehicles — Trailers up to 3,5 t —
Calculation of the mechanical strength
of steel drawbars
Véhicules routiers — Remorques jusqu’à 3,5 t — Calcul de la
résistance mécanique des timons en acier
Reference number
©
ISO 2012
© ISO 2012
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ii © ISO 2012 – All rights reserved

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols . 1
3.1 Terms and definitions . 1
3.2 Symbols . 2
4 Requirements . 3
4.1 Maximum of the vertical static force “S” . 3
4.2 Material and weldability of the drawbars . 3
4.3 Strength calculation . 3
Annex A (informative) Examples of configurations . 7
Bibliography .14
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 7641 was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 4, Exterior
fittings of car/trailer-caravan combinations.
This first edition of ISO 7641 cancels and replaces ISO 7641-1:1983, which has been technically revised.
iv © ISO 2012 – All rights reserved

INTERNATIONAL STANDARD ISO 7641:2012(E)
Road vehicles — Trailers up to 3,5 t — Calculation of the
mechanical strength of steel drawbars
1 Scope
This International Standard gives a simplified procedure for the calculation of the mechanical strength
of steel drawbars, whether there are welds or not, for centre-axle trailers Categories O1 and O2 as
specified in the UNECE, Consolidated Resolution on the Construction of Vehicles (R.E.3). Consequently, it
only applies to simple constructions that enable a calculation in bending.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
UNECE, Consolidated Resolution on the Construction of Vehicles (R.E.3)
3 Terms, definitions and symbols
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1.1
mechanical coupling device
mechanical coupling component
part fixed to the frame, to self-carrying parts of the bodywork and to the chassis of the tractor and the
trailers, used to couple the vehicles
NOTE 1 This includes parts used to attach the coupling device or the components to the vehicle or to actuate
the coupling device.
NOTE 2 Mechanical coupling devices transmit horizontal forces in the driving direction or the lateral direction.
Vertical supporting forces are also transmitted.
3.1.2
drawbar
separate technical unit attached to the frame of the trailer with or without inertia control devices and
comparable equipment parts at the front of the towed vehicles or at the vehicle chassis, adapted to couple
with the tractor with help of drawbar eyes, coupling heads of similar devices
NOTE 1 They are fixed in the vertical direction; they are able to receive vertical forces (rigid drawbars). Rigid
drawbars can be fixed completely rigid or by means of a suspension. Drawbars can be composed of more than one
component. They can be adjustable in height.
NOTE 2 Examples of configurations are shown in Annex A.
3.1.3
chassis part
part of the frame and the bodywork of the trailer, that participate in connecting the bodywork and its
load to the axle
3.1.4
simple drawbar
drawbar (3.1.2) composed of either
— two straight arms with open or closed profile with constant or decreasing cross section, or
— a single profile made of a closed constant or decreasing cross section, in which case it can be
composed of more than one component, adjustable in height
NOTE 1 Fundamentally there can be mounted inertia control devices or the coupling head/drawbar-eye to
the drawbars.
NOTE 2 In the case of simple drawbars, the mechanical resistance can be calculated with sufficient security, so
that a dynamic resistance test of the whole construction can be avoided.
3.1.5
centre-axle trailer
trailer having a drawbar (3.1.2) which cannot move in a vertical plane independent of the trailer and
having an axle or axles positioned close to the centre of gravity of the trailer, when uniformly loaded
NOTE The vertical force imposed on the coupling of the towing vehicle cannot exceed 10 per cent of the
maximum mass of the trailer, or 1 000 kg, whichever is the lesser.
3.2 Symbols
e distance, in metres, from the horizontal axis of the coupling device (coupling ball
centre) to the drawbar neutral fibre at the first fixing point to the trailer frame (see
Figure 1)
e distance, in metres, from the horizontal axis of the coupling device (coupling ball
x
centre) to the drawbar neutral fibre at the cross section corresponding to the
maximum strain rate (see Figure 1)
l distance, in metres, from the vertical axis of the c
...