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An American Looks at MI
Page 85
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Multi-ratio Gearboxes, as Generally Employed in the U.S.A., Recommended for British High-speed, Lorries
By Bryan A. Parker
SO long as Ml does not become integrated with any urban road system, it will be a fine start to a new national network. M1 appeared to me, on my recent visit to Britain, to be more like the German autobahns than the American freeways in that it is designed to serve traffic running between areas of the country rather than into and through cities.
America is already learning that some of its freeways will soon be carrying heavy volumes of purely local city traffic, rather than highspeed long-distance traffic for which they were originally designed.
British operators should not experience tyre problems if they choose the proper equipment for motorway work. One of our manufacturers has produced two new tubeless tyres to replace 20-in. and 22-in, covers of conventional type. Their sizes are 11-22.5-in. and 11-24.5-in.
• Average of 180° F.
The smaller tyre, loaded to its rated capacity of 4,880 lb. at recommended pressure, runs at an average temperature of 180° F. at a sustained 75 m.p.h. This is under normal climatic conditions. In desert country its temperature would reach 250° F., but even this is well below the point, 380° F., at which nylon begins to break down.
It would therefore appear that suitable tyre equipment for the British operator can be provided. A valuable accessory is a thermometer to indicate any undue rise in tyre temperature. Its value greatly exceeds its cost.
A tyre fire, should it occur, is extremely hard to put out. The only sure way is to immerse the tyre completely in earth or water. Merely to put out obvious flames or smouldering is not enough, for the fire would recur once the temperature built up again to the point of spontaneous combustion.
Among the acute problems which face American operators is that of brakes. This is particularly critical in mountainous country, and the police will stop any vehicle the brakes of which show the slightest sign of smoking. Devices such as water coolers and exhaust brakes have been tried, but only exhaust brakes seem to be acceptable, as other equipment is too heavy. Disc brakes would appear to be ideal for American conditions.
Although American law requires that front-wheel brakes be fitted, in actual practice drivers and operators slacken off the adjusters so that the brakes are inoperative on wet and icy roads. Front-wheel braking at high speed is dangerous.
In very low temperatures, the tensile strength of steel drops and fifth-wheel couplings have been known to fail. Lubricants have to withstand extremes of temperature. Tyres lose traction in cold weather to the extent of 15 per cent. at minus 20° F.
With high-speed operation it is difficult to arrive at an economic power rating which will enable fast average speeds to be maintained without excessive fuel consumption. I observed M1 traffic at a spot about 25 miles south of Rugby, about halfway up a gradient appromixately a third of a mile long. It seemed that those vehicles which passed me had only a main gearbox, because the engine speed could be heard to fall off rapidly at the gradient.
It seemed that engines were labouring before a lower ratio could be selected, and that the gearbox ratios were therefore too widely separated. In the United States the practice is to install 10or 12-speed gearboxes. In general, the gear splits are at approximately 250-300 r.p.m., and vehicles so equipped are able to maintain high average speeds and climb gradients quickly, thus reducing the nuisance of slow-moving traffic hindering normal flow.
Long Engine Life •
Over the years it has been shown that such vehicles have a long engine life and good fuel economy because the engines always operate well within their most efficient torque-h.p. range.
Slow overtaking on express highways is intolerable, and in California there is a law which states that there must be a difference of at least 11 m.p.h. between an overtaking vehicle and the one it is passing, whilst the complete rnanceuvre must be completed in no more than 1,320 ft.
Great importance is attached to cab comfort in the U.S.A., together with the adequacy of rear-view mirrors, the standard size of which is 1 ft. 3 in. by 5 in. Efficient heaters are, also common. The British practice of driving on side lights only would invite immediate arrest in America. I thought that the side'and rear lights of British vehicles were inadequate, and that lamps should be fitted to each corner of a vehicle.
Drivers in big American companies are required to stop every 100 miles to check oil and water levels, tyre pressures, ropes, and trailer and pneumatic brake couplings. Every goods vehicle is required to carry certain safety equipment including a fire extinguisher, spare bulbs and fuses, hand tools and warning devices for use when stationary in an emergency.
These consist of red magnesium flares which burn for 20 minutes, paraffin flare tots or reflectors. Three warning signs are required, one to be placed 100 ft. ahead of the disabled vehicle, another 100 ft. behind and the third 10 ft. from the vehicle and 3 ft. to the off side.
Drivers Must be Fit High-speed driving requires men with -special training, and in good physical condition. The Interstate Commerce Commission have set minimum standards of vision, hearing and general fitness to which all drivers must conform, and all bus and lorry drivers must pass a medical examination at least every three years. Certificates are issued to them and they must always be carried.
Travel fatigue becomes critical at speeds above 60 m.p.h. and insurance companies' records show that serious accidents frequently occur on straight stretches of road. The generally adopted 50 m.p.h. speed limit has been arrived at after many years of study. Several companies have their own patrol cars which report on any driver's violation of speed limits, and other malpractices.
Most American vehicles have both road-speed and engine-speed recorders. These are regarded as safeguards for both employer and employee. Drivers and their unions favour them as men are paid from charts, and the information they provide is accepted as evidence whenever necessary in courts of law. The charts are also useful to maintenance engineers as they record up to lm. miles and 999m. engine revolutions.
From my conversations with several British lorry drivers, I gathered that most seemed to think that two-speed axles were acceptable, but they were not keen about multi-ratio transmission systems with two gear levers to operate.