Directive 94/20/EC of the European Parliament and of the Council (repealed)Show full title

4.1. Coupling balls and towing brackets

4.1.1.The mechanical coupling devices of coupling balls may be of the following types:

• one-piece coupling balls including devices with non-interchangeable detachable balls (see Figure 20),

• coupling balls, comprising a number of parts which can be dismantled (see Figures 21, 22, 23),

• towing brackets (see Figure 24).

4.1.2.The basic test is an endurance test with an alternating test force. The test specimen is the coupling ball, the ball neck and the mountings necessary for attaching to the vehicle. The coupling ball and towing brackets must be rigidly mounted to a test rig, capable of producing alternating forces, in the actual position in which it is intended for use.

4.1.3.The positions of the fixing points for attaching the coupling ball and towing brackets are specified by the vehicle manufacturer (see Annex VII, Section 1.2).

4.1.4.The devices submitted to the test shall be provided with all design details which may have an influence on the strength criteria (for example electrical socket plate, any marking, etc.). The test periphery ends at the anchorage points or fitting points. The geometric location of the coupling ball and the fixing points of the coupling device related to the reference line shall be provided by the vehicle manufacturer and shall be shown in the test report. All relative positions of the anchorage points with respect to the reference line, for which the towing vehicle manufacturer shall provide all the necessary information to the towing device manufacturer, shall be repeated on the test bed.

4.1.5.The assembly mounted on the test bed shall be subjected to a test on an alternating stress tensible testing machine (for example on a resonance pulser).

The test load shall be an alternating force and must be applied to the coupling ball at an angle of 15^o ± 1^o as shown in Figure 17 and/or Figure 18.

If the ball centre is above that line parallel to the reference line as shown in Figure 19 which contains the highest of the nearest fixing points, the test has to be carried out with an anlge α = -15^o ± 1^o (see Figure 17). If the ball centre is below that line parallel to the reference line as shown in Figure 19 which contains the highest of the nearest fixing points, the test has to be carried out with an angle α = + 15^o ± 1^o (see Figure 18).

This angle is chosen in order to take account of the vertical static and dynamic load. This test method is only applicable to a permitted static load of not more than

If a static load above 120 · D is requested, the test angle should be increased to 20^o. The dynamic test must be performed with the following test force:

F_{hs res} = ± 0,6 D

4.1.6.The test procedure is applicable to the different types of coupling devices (see Section 4.1.1) as follows:

4.1.6.3.Coupling devices with variable dimensions e and f for demountable and interchangeable coupling balls.

4.1.6.3.1.The strength tests for such towing brackets (shown in Figure 25) shall be carried out to the requirements of Section 4.1.5.

4.1.6.3.2.If a worst case configuration can be defined by agreement between the manufacturer and the Technical Service, the testing of this one configuration alone shall be sufficient. Otherwise, several ball positions shall be tested in a simplified test programme according to Section 4.1.6.3.3.

4.1.6.3.3.In a simplified test programme, the value for f shall be between a defined value of f_min and a value of f_max which does not exceed 100 mm. The ball shall be at a distance (e_max) of 130 mm from the support. To cover all possible positions of the ball, in the field given by the horizontal distance from the mounting surface and the vertical range of f (f_min to f_max), two devices are to be tested:

• one with a ball in top (f_max,), and

• one with a ball in low (f_min) position.

If the field of possible ball positions is divided by the line parallel reference line (see Figure 25c), the test angles are:

• α for the ball above, and + α for the ball below that reference line (compare Figure 19).