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THREE INTO TWO
Page 74
Page 75
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WON'T GO by Gibb Grace
ONE of the basic aims of EEC harmonization in the vehicle field has been to introduce a mutually acceptable type approval system. Such a Community as opposed to national — system ultimately will ensure that a vehicle built anywhere in the EEC will comply with the Community regulations and can thus be sold without restriction anywhere within the market. This goal is still a long way off but a start has been made and some minor regulations have already been adopted. The regulation 71 /320 /EEC dealing with vehicle braking systems is one such item; it was adopted by the Six on March 1 1973 and by Britain on July 1 this year.
The EEC regulations do not immediately take over from C and U and in fact no date has been given for when they officially do, but the adoption of the EEC regulations does mean that they will be permitted as an alternative to the C and U Regulations from July 1 1973 onwards.
Therefore it is possible in theory for a German manufacturer, say, whose vehicle has a type-approved two-line brake system to sell that vehicle legally in Britain. The same, of course, applies to British manufacturers; they can build and sell type-approved two-line vehicles in Britain and throughout the EEC.
Despite what has appeared elsewhere in the technical press the adoption of the EEC regulation will cause operators in Britain little concern as the requirements laid down at this stage are binding on manufacturers only and it is up to them to see that the vehicles they build comply.
A major topic of discussion even now in respect of EEC braking is the prospect of Britain having to revert to the two-line brake system for artics (or drawbar combinations) that we abandoned some time ago. The C and U Regulations do not specifically require a three-line system but they do demand an independent secondary system and UK designers decided that the only practical solution was to use a third line. In the same way the EEC regulation permits the use of two or three-line systems as it simply states "shall have two or more lines". It may seem incredible that such a basic requirement should be left in the air but an ISO committee has been set up on articulated vehicle and semi-trailer compatibility and the interested parties are hopeful that a decision in favour of one system or the other will eventually be made.
Britain and France are the only two countries in the world, let alone Europe, to use the three-line system and it does rather look as if we shall be the ones who have to make the change. The two systems are based on different priorities which to some extent may reflect the differences between vehicle operation in Britain and the Continent.
The C and U Regulations are designed so as to leave a vehicle immobilized after a brake failure — stranded until a qualified mechanic can deal with the fault.
Residual performance
The EEC regulations require, on the other hand, that some residual performance is available at the foot-brake even after a failure so that the driver can get the vehicle back to base or at least to a service point albeit with brakes having a reduced performance. This is achieved quite simply by siting system protection valves at each reservoir. If a reservoir fails, for example, air is lost only from that one point and the compressor will continue to charge the remaining tanks.
The two-line system suffers, however, from having no secondary trailer braking; a failure of a trailer brake diaphragm, for example, would mean that the vehicle had no trailer brakes. Such a failing would not go unnoticed by the driver, of course, as a warning light or buzzer would alert him of the danger. Mixing twoand three-line tractive units and semi-trailer is bound to cause difficulties in any change-over period although, as pointed out, these problems already occur between, say, Germany and France and have presumably been solved by local modifications. A two-line tractive unit can couple without problem to a three-line system semi-trailer but a threeline tractive unit cannot safely couple to a two-line semi-trailer as the trailer will be without secondary brakes. The trailer still has an emergency system in that trailer breakaway causes the trailer brakes to be applied.
Theoretically, the three-line system may be safer but there is no hard evidence in practice to prove the point one way or the other. What is certain is that the two-line system is basically simpler and is therefore cheaper to install and easier to maintain, so the net result could be better than might be supposed.
As mentioned earlier, true mutually acceptable type approval is still a long way off, for at the moment the EEC regulations cover only the performance aspect of braking and not, for example, specifications of individual items such as reservoirs. Where no EEC regulation exists the controlling regulation is that of the country in which the vehicle is to be sold and thus for the time being at least the spirit of the EEC is sadly undermined.
To take the example of reservoirs a little further, Germany will accept dual reservoirs (that is two tanks made out of one by adding a separating plate) but France will not, and these types have to be separately approved by each of the countries concerned. The problem is compounded further when we consider something as basic as a thread form. At the moment ISO, BSP and metric threads are used within the EEC and some countries require bosses on the tanks to take a flat sealing washer whereas others will accept the conical dry-seal type. Such international skulduggery need not worry British operators but it is interesting to see just how entrenched national peculiarities are behind the general air of entente cordiale.
From a performance point of view the braking requirements are defined in a different way — a minimum braking distance for a given speed is stipulated in place of a minimum peak brake efficiency — but the level of performance required is no harder to achieve.
The EEC requirements cover such things as the time taken for the engine compressor to charge the system to a working level from empty, and the brake response time. These points are not covered in C and U Regulations but are a feature of the industry's own Code of Practice. The precise method of measurement differs between EEC and Code of Practice but the EEC requirements are generally considered to be as stiff as Code of Practice requirements.
A basic difference is that under the EEC regulations a performance requirement is given for a variety of vehicle types and gross weights. Psv and goods vehicles are each divided into three groups and minimum stopping distances for primary and secondary brake systems are given for each case — see the accompanying table.
Braking distance CM road tests always include the braking distance required to stop from 30 mph and it is significant that all the vehicles we have tested over the last few years would easily better the EEC requirements. By way of comparison, in the Ni range for example (requirement 174ft at 43.5 mph) the British Leyland Austin Morris 7cwt van achieved 54.3ft from 40 mph; in the N2 range (requirement 95.9ft from 31.3 mph) the British Leyland Terrier TR 750 achieved 56.7ft from 30 mph;