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THE FUTURE OF VEHICLE DESIGN,

23rd May 1922, Page 13
23rd May 1922
Page 13
Page 14
Page 13, 23rd May 1922 — THE FUTURE OF VEHICLE DESIGN,
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Which of the following most accurately describes the problem?

A Summary of a Paper on the Future Design of Road Vehicles for Goods and Passenger Service Read at the Institute of Transport,

By Sir John E. Thornycroft, KB.E.

A• FTER going very carefully into the question of the design of present-day road vehicles, Sir John E. Thornycroft asserted that he had come to the conclusion that, until the physicists and

chemists discover some new source of energy or means of storing it, he did not think it probable that. there would be any great change. Engineers will have to content themselves with devoting their attention to improving details of design with a view to getting the best possible economy out of the fuel available and making the motors as simple as possible to maintain.

It was in order to see what would be the probable developments in the commercial motor vehicle, from the point of view of the designer and builder, that Sir John Thornyeroft set out the various considerations underlying the problem Those who are responsible for organizing, transport to-day seem quite definitely to have come to the conclusion that, in this country, it is only economical to use horses as locomotives in special eases, and such serious competition has grown up between. the road vehicle and the railway that, at the present time, railways are seeking additional powers to run road vehicles themselves.

Numerous factors have contributed to the success of the present-day motor vehicle, the chief being (1) the development of the light, internal combustion engine, so rapidly and so widely adopted owing to the now almost universal supplies of petrol and fuel, (2) the introduction of greatly improved steels permitting higher stresses and a light vehicle to be constructed. to perform a given service, and (3) the use of indiarubber tyres permitting higher speeds without damage and, consequently, giving much more .economical results. Loads have not increased to the extent that had been originally expected, but speed has increased very greatly. The steam vehicle. aA one time led the way for the heavy loads, but the advantages of the petrol engine have resulted in steam vehicles being outnumbered.

The Accepted Scheme of Petrol Vehicle Design.

The general scheme of the design of petrol vehicles is, to all intents and purposes, the same throughout the industry, viz., an internal combustion engine in front of the vehicle, a disconnecting clutch, a series of different gears and the driving axle in the rear. The weight of the chassis is proportionate to the load carried, the proportion being fairly constant throughout the different sizes.

Sir John E. Thornycroft went over the respective merits of the steam, petrol and electric vehicles, and then went on to deal with the electrically driven vehicle taking its source of power from an overhead conductor in the same way as a tramc,ar does. He said that it seemed improbable that a vehicle driven in this way will ever come into general use for carrying goods, but for passenger work it seems probable that there will be a very considerable development owing to the vehicles combining the advantage of obtaining power direct from a central power station (which must. necessarily be much more economical than power generated by small, individual motors), and having the freedom of an independent vehicle to move anywhere on the road so long as there are electric conductors.

Dealing with the question of different types of fuels, Sir John showed that the designer and builder

may be limited by the impossibility of obtaining a particular fuel at economical prices, and he considers that, where petrol is available, it will always secure favour when it is obtainable at anything like a reasonable price, users not being prepared to put up with the extra trouble which some cheaper fuel entails. Kerosene, in some parts of the world, is materially cheaper than petrol, and there is a fair number of vehicles using it, but it cannot be said that there has been any general adoption. Where alcohol is available, by increasing the compression of the motors they can be run on it quite well and, in the event of a world shortage of petroleum spirit, this must be looked upon as one of the best. substitutes. Quite new methods of low-temperature distillation of coal. give promise of greater supplies of benzole, which is, of course, an excellent substitute for petroleum ,spirit. A very great gain in economy should be produced by running motors on producer gas made by burning anthracite or some similar fuel. In parts of the world where petrol cost is high, or where fuel is difficult to obtain, there would seem to be a probability of considerable development in the use of producer gas, as in these undeveloped countries there are generally supplies of charcoal at a low price, and this forms the best possible fuel for a. gas producer.

Relative Thermal Efficiency. Sir John E. Thornycroft showed that there have been material developments in the design and manufacture of steam vehicles, but the advance with this type has been less than the progress which has been made with the internal-combustion-engined vehicle. If one expressed the fuel consumption per ton miles in terms of heat units available in the fuel, it will be found that the average figures of the steamers run in the Liverpool trials in 1801 were 18,350 B.T.U.s per gross ton mile, and the . present-day figures of the best types in general use show a consumption of 17,600 B.T.U.s. In the 1901 trials the internalcombustion-engined vehicles showed up very favourably in comparison with the steam vehicles, averaging 33,6 ton miles to the gallon of petrol, or, expressed. in heat units, 3,600 B.T.U.s per grass ton mile. Taking the average present-day consumption at 10 or 15 per cent, less than the best recorded results, we have 2,450 B.T.U.s per gross ton mile, which shows a really important advanceand is of great interest when compared with the corresponding figure of 17,600 B.T.U.s of the present-day steam vehicles. The thermal efficiency of an engine when burning suction •gas stands at about 4,500 B.T.U.s per gross ton mile, and the steam vehicle designs which have survived all employ a boiler holdirig a considerable volume of water, the flash boilers of the Serpollet type having entirely disappeared.

The Limitations of the Electric Vehicle.

Although the great development in the use of electric vehicles anticipated in America a few years ago has not been realized, there is a definite future before the electric vehicle, but, with the present form of storage battery, its radius and speed are too, small to enable it to compete with the vehicle fitted with an internal-combustion engine. For congested town traffic and to avoid blocks in the traffic, it is probable that, in the near future, there will be a low speed limit as well as a high. Returning.to petrol vehicles and dealing with the components in the present-day type of chassis, Sir John said that, while chain gear is still employed in some case-, it is certain that it is being displaced by gear transmission. He did not refer at all to vehicles with more than two axles, but with regard to transmission ..of the drive through all the wheels of a four-wheeled vehicle ; he regarded this system as having great advantages, but thought that it was highly probable that, when it was required to run over unmade roads or cross-country, it would be more economical to use an ordinary lorry drawn by a special tractor.

The Future of Design.

Considering the future of design, he asked the question, what are the most likely features to be modified? Running costs are largely made up of

fuel consumptionand maintenance. There is no reason why a highly efficient motor and gearing should not exist with a minimum maintenance cost, and with the best designs it, may be taken for granted that it does, but it is a -Very nice point for the designer so to proportion the parts of his mechanism that he does not make the size of the various parts so large, in order to reduce the stress and wear, that he unduly increases the weight of hismachine and its consumption of fuel.

He did not look forward to any great improvement on the best of the present-day engines in the near future. As regards transmission, every conceivable arrangement has been tried and patented, but the simplest has survived. The epicyclic gear is satisfactory where there is only one change required, or where constant change is necessary.

The only alternative to the gearbox transmission which has met with any success for commercial vehicles seems to be the tevensi electric drive.. He dealt briefly with the merits of this particular type, and then went on to refer to the question of combining the engine and gearbox in the single unit. Whilst this arrangement has undoubted advantages in the first cost of manufacture, and would seem' in many cases, theoretically right, in practice it has not, proved the best. for commercial vehicles, largely because of the desire on the part of owners of large fleets to substitute complete new units in the case of a temporary failure.

The Prospects of the Diesel Engine for Road Transport.

He thought that if a small Diesel engine could be made with a, suitable range of power and revolutions, it would be a great stride, and not, only most useful for 'motor vehicles, but for all sorts of other purposes, but experience with motors of this type ranging over a number of years does not make' it eeem at all probable that we. shall have motors of this type fitted to lorries at an early date. There, seems a probability that it will he possible to employ aluminium to a greater extent in the near future owing to the improvements in its alloys which are being made. A short time ago it would have been looked upon as impossible to use cast aluminium road wheels, but they have been in service now on a number of vehicles with success for a considerable time. Should it be possible to use pneumatic tyres, there is no doubt that many parts of the vehicle at present made in steel would hold up satisfactorily in a suitable aluminium alloy.

Dealing with the question of solid tyres versus pneumatics, Sir John holds that, with the present cost of pneumatic tyres, it is very doubtful if it is worth while using them in the case of passenger vehicles and lorries taking fairly heavy loads, for the pressure required in the tyres is so great that the shocks to the road do not seem to lio. so very much less. From trials which have been made, it seems difficult to prove by measurements that the pneumatic tyre greatly reduces the vertical motion of the vehicle by absorbing the bumps and inequalities of the road surface, but there is no question that the sensation when riding on pneumatic tyres is very much easier, many of the innumerable small jars and stresses which would be transmitted to the vehicle being absorbed by the tyres. Failing a great reduction in first cost and a lessening of some of the other disadvantages, it did not seem probable that there would be any greatly extended use for pneumatic tyres on the heavier class of vehicles.

The Desirability of Weight Saving in Bodies.

With the exception of the London General Omnibus Co.., few designers have done their best to save weight in the case of bodywork, in either passenger or goods vehicles. Large carriers and railway companies are row finding it economical to make up their loads on special platforms or in containers, which are handled by cranes or on wheeled trollies in the yards and depots, and then placed completely laden on the chassis to be conveyed to another centre. The weight. of these containers is often a very large proportion of the load and, to obtain really economical results with this system, it is evident that oonsid.erable improvement must be made. Mechanical handling devices are now being called for to a large extent, power tipping gears and cranes being the most frequently employed. • Experience with tipping devices is hardly sufficient yet to enable anyone to say whether a mechanical drive from the motor itself or the hydraulic system operated by a pump driven from the motor will prove the better, but there seems to be indications that the hydraulic system is in favour, except for electric vehicles where an independent electric motor is obviously the most suitable.

There does not now seem to be the need for providing the same accessibility 0 the engines of steam vehicles, but it is still very desirable to be able readily to inspect them. There is no doubt that this is the reason for what may be looked upon as the present standard design of steam vehicles, but in the larger passenger vehicles, and in those for transporting heavy goods, there is a tendency to give less space in the front. of the vehicle to the motor, and there is every probability of the arrangement in which the drive is placed alongside the motor, instead of behind it, being further developed, as it allows more even load distribution.

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Organisations: Institute of Transport
Locations: Liverpool

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