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2nd June 1972, Page 86
2nd June 1972
Page 86
Page 86, 2nd June 1972 — artics and
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Which of the following most accurately describes the problem?

trailers

DIN OR ISO BRA

WHETHER drawbar outfits will become as widespread as on the Continent remains to be seen, but their use is growing and it is worthwhile looking at some Continental drawbar equipment and noting the current trends.

Many drawbar vehicles here suffer from. what I call push and shove, ie the trailer moves backwards and forwards relative to the truck owing to a loose connection and causes an irritating sensation for the driver. The relative movement also causes wear and produces noise.

Britain does not have the same depth of drawbar operating experience as the Continent and no standard design of towing eye and pin has been laid down. A very common arrangement even today is the "hook and eye" developed during the Second World War for military trucks and trailers, guns, etc. The design used a 34in. diameter ring on the trailer which simply dropped over a U-shaped hook on the towing vehicle and was held there by a spring-loaded catch. Perhaps surprisingly, this 3iin. ring is still being used in drawbar trailers and dollies currently being manufactured today.

To make matters worse they are often used in conjunction with a clevis and pin of about ltin. diameter. It is not hard to imagine the snatching and pin wear that such a set-up causes.

Better commercial designs are available but again these tend to be made to the manufacturer's standard rather than to an international standard and the proliferation of designs will ultimately lead to coupling problems. It is significant that the success of the artic is in no small way due to the early decision to adopt the American 2in. pin standard.

In Europe, where the drawbar unit has flourished, a standard towing eye and pin was adopted as far back as the 1930s. This standard design which uses a 38rnm pin and 40mm towing eye, is still in use today and. has been taken as the standard German design, ie the DIN standard.

However, the DIN standard gradually lost favour with the Scandinavians, who with gross train weights up to 50 tons and higher needed a stronger coupling. Also the 2mm play inherent in the design led to premature wear and Sweden went on to establish its own standard based on 57.5mm diameter eye.

The subsequent problems encountered in swopping drawbar trailers throughout Europe convinced everyone concerned of the need for a common standard and one eventually was produced under an International Standards Organisation (ISO) committee. This standard has compromised the Swedish and DIN dimensions and calls for a 50mm diameter towing eye and a 49.2 to,49.5mm pin, ie a tolerance of only 0.5 to 0.8mm. A towing eye and pin designed to these limits has a train load capacity of up to 50 tons — high enough for the whole of Europe and almost eliminating relative movement and thus wear.

It is important to point out that at the time the new ISO Standard was adopted a substantial proportion of Europe — particularly in France and Germany — used the DIN coupling and faced considerable capital outlay to change vehicles over to ISO. But so strong was the argument for uniformity that they have or are in the process of changing over. It follows that a British operator who wants to take full advantage of interchanging with European trailers should make sure he has approved ISO design equipment.

A leading manufacturer of drawbar hitches is VBG Produkter KB of Sweden. VBG has made towing hitches for 30 years and now holds 75 per cent of the Scandinavian market and some 90 per cent in Sweden. VBG products are available in the UK through the sole UK importer, John R. Billows (Sales) Ltd, of Kettering. VBG model 800 automatic hitch is designed to the ISO standard and because of its very tight tolerance — approximately 0.5mm play — has a very long working life. The company gives a written guarantee against wear of any sort occurring within 125,000 miles but says that in its experience and its customers', even this figure is conservative. A feature of the design is that the only moving parts are the actual bolt and its lift lever; the bolt itself is coated with an anti-wear agent called Manganite.

Driver-only

Since the law which required a driver to have a mate on drawbar operations has been rescinded the need for a coupling which can be operated by the driver alone has become of prime importance. Again, the VBG 800 coupling is capable of driver-only coupling provided a balanced drawbar is used. •

To couple up, the driver first lifts the operating lever then backs on to the drawbar which is funnelled into the locking position by the specially shaped jaws. When the towing eye is right home, the bolt is lifted the last +in. which allows it to drop through the eye and lock. Unless the drawbar is properly home the bolt will not operate. Pin and eye are designed to cope with a 50-ton-train weight or a maximum combination weight of 70 tons; the hitch itself will withstand a load of 12 tons without failure.

VBG also manufactures a drawbar which has an inbuilt secondary truck /trailer connection. This type of safety drawbar, which is required by law in Sweden, is available in three lengths, 6, 7 and 8ft, and conforms to the relevant Swedish safety standards SMS 2333 and SMS 2334. All designs are suitable for vehicle gross combination weights of up to 70 tons.

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People: DIN OR ISO BRA

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